Display device and operation method thereof

ABSTRACT

A flexible display device with high viewability is provided. The display device includes a first substrate, a second substrate, a first element layer, and a second element layer. The first element layer is positioned between the first substrate and the second substrate. The second element layer is positioned between the first substrate and the second substrate. The first element layer and the second element layer overlap with each other in a region. The first substrate and the second substrate have flexibility. The first element layer includes a display element and a first circuit. The display element is electrically connected to the first circuit. The second element layer includes a sensor element. The sensor element has a function of sensing distortion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

One embodiment of the present invention relates to a semiconductordevice and a display device including the semiconductor device.

Note that one embodiment of the present invention is not limited to theabove technical field. The technical field of one embodiment of theinvention disclosed in this specification and the like relates to anobject, a method, or a manufacturing method. In addition, one embodimentof the present invention relates to a process, a machine, manufacture, aprogram, or a composition of matter. Specifically, examples of thetechnical field of one embodiment of the present invention disclosed inthis specification include a semiconductor device, a display device, aliquid crystal display device, a light-emitting device, a lightingdevice, a power storage device, a memory device, a method for drivingany of them, and a method for manufacturing any of them.

In this specification and the like, a semiconductor device generallymeans a device that can function by utilizing semiconductorcharacteristics. A transistor and a semiconductor circuit areembodiments of semiconductor devices. In some cases, a memory device, adisplay device, or an electronic device includes a semiconductor device.

2. Description of the Related Art

A transistor including a semiconductor thin film is applied to a widerange of electronic devices such as an integrated circuit or a displaydevice. A silicon-based semiconductor material is widely known as amaterial for a semiconductor thin film applicable to the transistor. Asanother material, an oxide semiconductor has been attracting attention.

For example, a transistor whose active layer includes an amorphous oxidesemiconductor containing indium (In), gallium (Ga), and zinc (Zn) isdisclosed in Patent Document 1.

For a display device, it is required to improve the flexibility orimpact resistance besides a reduction in the thickness and weight. Forexample, Patent Document 2 discloses a flexible active matrixlight-emitting device in which an organic EL element and a transistorserving as a switching element are provided over a film substrate.

REFERENCE Patent Document

[Patent Document 1] Japanese Published Patent Application No.2006-165528

[Patent Document 2] Japanese Published Patent Application No.2003-174153

SUMMARY OF THE INVENTION

Application of a flexible display device utilizing its flexibility as ina curved display or the like is expected. Meanwhile, intentional orunintentional change in the shape of a display during display operationreduces display viewability in some cases.

It is an object of one embodiment of the present invention to provide adisplay device with high viewability. Another object is to provide aflexible display device. Another object is to provide a lightweightdisplay device. Another object is to provide a display device with highreliability. Another object is to provide a novel display device or thelike. Another object is to provide an operation method of the displaydevice. Another object is to provide a program for operating the displaydevice. Another object is to provide a novel semiconductor device or thelike. Another object is to provide an operation method of thesemiconductor device or the like. Another object is to provide a programfor operating the semiconductor device or the like.

Note that the descriptions of these objects do not disturb the existenceof other objects. In one embodiment of the present invention, there isno need to achieve all the objects. Other objects will be apparent fromand can be derived from the description of the specification, thedrawings, the claims, and the like.

One embodiment of the present invention relates to a flexible displaydevice including a distortion sensor.

One embodiment of the present invention is a display device including afirst substrate, a second substrate, a first element layer, and a secondelement layer. The first element layer is positioned between the firstsubstrate and the second substrate. The second element layer ispositioned between the first substrate and the second substrate. Thefirst element layer and the second element layer overlap with each otherin a region. The first substrate and the second substrate haveflexibility. The first element layer includes a display element and afirst circuit. The display element is electrically connected to thefirst circuit. The second element layer includes a sensor element. Thesensor element has a function of sensing distortion of the firstsubstrate or the second substrate.

In this specification, ordinal numbers such as “first”, “second”, andthe like are used in order to avoid confusion among components, and theterms do not limit the components numerically.

The second element layer may include a second circuit, and the secondcircuit may be electrically connected to the sensor element.

One embodiment of the present invention is a display device including afirst substrate, a second substrate, and an element layer. The elementlayer is positioned between the first substrate and the secondsubstrate. The first substrate and the second substrate haveflexibility. The element layer includes a display element, a sensorelement, a first circuit, and a second circuit. The display element iselectrically connected to the first circuit. The sensor element iselectrically connected to the second circuit. The sensor element has afunction of sensing distortion of the first substrate or the secondsubstrate.

The first circuit and the second circuit may each include a transistorin which a channel formation region includes an oxide semiconductor.

The oxide semiconductor preferably contains In, Zn, and M (M is Al, Ti,Ga, Sn, Y, Zr, La, Ce, Nd, or Hf).

The oxide semiconductor preferably includes a c-axis aligned crystal.

As the sensor element, a metal thin film resistor can be used.

As the display element, an organic EL element can be used.

One embodiment of the present invention is an operation method of adisplay device, which includes a first step of acquiring image data toform a virtual screen; a second step of acquiring data on a shape of adisplay portion to form a three-dimensional shape model; a third step ofacquiring positional data of a viewer to regard the three-dimensionalshape model as a two-dimensional display portion and to assign acoordinate to the two-dimensional display portion; a fourth step ofperforming calculation to determine a portion of the display portion notseen from a position of the viewer; a fifth step of converting acoordinate of the virtual screen to the coordinate of thetwo-dimensional display portion; and a sixth step of outputting imagedata obtained in the fifth step to the display portion.

One embodiment of the present invention is an operation method of adisplay device, which includes a first step of acquiring image data toform a virtual screen; a second step of sensing a status of the displaydevice and a status of a viewer; a third step of acquiring data on ashape of a display portion to form a three-dimensional shape model; afourth step of acquiring positional data of the viewer to regard thethree-dimensional shape model as a two-dimensional display portion andto assign a coordinate to the two-dimensional display portion; a fifthstep of performing calculation to determine a portion of the displayportion not seen from a position of the viewer; a sixth step ofconverting a coordinate of the virtual screen to the coordinate of thetwo-dimensional display portion; and a seventh step of outputting imagedata obtained in the sixth step to the display portion. The second toseventh steps are performed one by one.

The second step of sensing the status of the display device and thestatus of the viewer may include an eighth step of determining whetherthe shape of the display portion is changed or not; a ninth step ofdetermining whether the position of the viewer is changed or not; and atenth step of determining whether an image change instruction is issuedor not. Here, operation proceeds to the third step when the shape of thedisplay portion is changed in the eighth step, whereas the operationproceeds to the ninth step when the shape of the display portion is notchanged in the eighth step; the operation proceeds to the fourth stepwhen the position of the viewer is changed in the ninth step, whereasthe operation proceeds to the tenth step when the position of the vieweris not changed in the ninth step; and the operation proceeds to thefirst step and proceeds to the sixth step after the first step isperformed when the image change instruction is issued in the tenth step,whereas the operation returns to the second step when the image changeinstruction is not issued in the tenth step.

In the above mode of the operation method of the display device,operation of returning from the seventh step to the second step may beperformed.

According to one embodiment of the present invention, a display devicewith high viewability can be provided. Alternatively, according to oneembodiment of the present invention, a flexible display device can beprovided. Alternatively, according to one embodiment of the presentinvention, a lightweight display device can be provided. Alternatively,according to one embodiment of the present invention, a display devicewith high reliability can be provided. Alternatively, according to oneembodiment of the present invention, a novel display device or the likecan be provided. Alternatively, according to one embodiment of thepresent invention, an operation method of the display device can beprovided. Alternatively, according to one embodiment of the presentinvention, a program for operating the display device can be provided.Alternatively, according to one embodiment of the present invention, anovel semiconductor device or the like can be provided. Alternatively,according to one embodiment of the present invention, an operationmethod of the semiconductor device or the like can be provided.Alternatively, according to one embodiment of the present invention, aprogram for operating the semiconductor device or the like can beprovided.

Note that the description of these effects does not disturb theexistence of other effects. One embodiment of the present invention doesnot necessarily achieve all the effects listed above. Other effects willbe apparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are cross-sectional views illustrating display devices.

FIGS. 2A and 2B are top views illustrating a display device.

FIGS. 3A and 3B are a cross-sectional view illustrating a display deviceand a top view illustrating a distortion sensor element.

FIG. 4 is a cross-sectional view illustrating a display device.

FIG. 5 is a block diagram illustrating a display device.

FIGS. 6A to 6F illustrate display modes.

FIGS. 7A and 7B illustrate a display mode.

FIGS. 8A and 8B illustrate distortion sensor circuits.

FIG. 9 illustrates a distortion sensor circuit and a pixel circuit.

FIG. 10 illustrates a distortion sensor circuit and a pixel circuit.

FIG. 11 illustrates a distortion sensor circuit and a pixel circuit.

FIG. 12 illustrates a distortion sensor circuit and a pixel circuit.

FIG. 13 illustrates a read circuit.

FIG. 14 illustrates a distortion sensor circuit and a pixel circuit.

FIG. 15 illustrates a distortion sensor circuit and a pixel circuit.

FIGS. 16A and 16B are cross-sectional views illustrating transistors.

FIGS. 17A and 17B are cross-sectional views illustrating transistors.

FIGS. 18A and 18B are cross-sectional views illustrating transistors.

FIGS. 19A and 19B are cross-sectional views illustrating transistors.

FIGS. 20A and 20B are cross-sectional views illustrating transistors.

FIGS. 21A and 21B are cross-sectional views illustrating transistors.

FIGS. 22A and 22B are cross-sectional views illustrating transistors.

FIGS. 23A and 23B are cross-sectional views illustrating transistors.

FIGS. 24A and 24B are top views illustrating transistors.

FIG. 25 is a perspective view illustrating a display module.

FIGS. 26A and 26B illustrate an example of a touch panel.

FIGS. 27A, 27B1, 27B2, and 27C illustrate examples of structures of asensor circuit and a converter and an example of a driving method of thesensor circuit.

FIGS. 28A to 28C illustrate an example of a sensor circuit.

FIG. 29 is a cross-sectional view illustrating a touch panel.

FIGS. 30A to 30C illustrate a structure of a data processing device.

FIGS. 31A to 31D illustrate electronic devices.

FIG. 32 illustrates operation of a display device.

FIG. 33 is a flow chart of operation of a display device.

FIG. 34 is a flow chart of operation of a display device.

FIG. 35 is a flow chart of operation of a display device.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will be described in detail with reference to drawings. Notethat the present invention is not limited to the following descriptionand it will be readily appreciated by those skilled in the art thatmodes and details can be modified in various ways without departing fromthe spirit and the scope of the present invention. Therefore, thepresent invention should not be interpreted as being limited to thedescription of embodiments below. Note that in structures of the presentinvention described below, the same portions or portions having similarfunctions are denoted by the same reference numerals in differentdrawings, and description thereof is not repeated in some cases. It isalso to be noted that the same components are denoted by differenthatching patterns in different drawings, or the hatching patterns areomitted in some cases.

Note that in this specification and the like, when it is explicitlydescribed that X and Y are connected, the case where X and Y areelectrically connected, the case where X and Y are functionallyconnected, and the case where X and Y are directly connected areincluded therein. Here, X and Y each denote an object (e.g., a device,an element, a circuit, a wiring, an electrode, a terminal, a conductivefilm, or a layer). Accordingly, a connection relationship other thanthose shown in drawings and texts is also included without limitation toa predetermined connection relationship, for example, the connectionrelationship shown in the drawings and the texts.

For example, in the case where X and Y are electrically connected, oneor more elements that enable electrical connection between X and Y(e.g., a switch, a transistor, a capacitor, an inductor, a resistor, adiode, a display element, a light-emitting element, or a load) can beconnected between X and Y. A switch is controlled to be on or off. Thatis, a switch is turned on or off (is brought into an on state or an offstate) to determine whether current flows therethrough or not.Alternatively, the switch has a function of selecting and changing acurrent path.

For example, in the case where X and Y are functionally connected, oneor more circuits that enable functional connection between X and Y(e.g., a logic circuit such as an inverter, a NAND circuit, or a NORcircuit; a signal converter circuit such as a DA converter circuit, anAD converter circuit, or a gamma correction circuit; a potential levelconverter circuit such as a power supply circuit (e.g., a step-upcircuit or a step-down circuit) or a level shifter circuit for changingthe potential level of a signal; a voltage source; a current source; aswitching circuit; an amplifier circuit such as a circuit that canincrease signal amplitude, the amount of current, or the like, anoperational amplifier, a differential amplifier circuit, a sourcefollower circuit, or a buffer circuit; a signal generation circuit; amemory circuit; and/or a control circuit) can be connected between X andY. Note that for example, in the case where a signal outputted from X istransmitted to Y even when another circuit is interposed between X andY, X and Y are functionally connected.

Note that when it is explicitly described that X and Y are connected,the case where X and Y are electrically connected (i.e., the case whereX and Y are connected with another element or another circuit positionedtherebetween), the case where X and Y are functionally connected (i.e.,the case where X and Y are functionally connected with another elementor another circuit positioned therebetween), and the case where X and Yare directly connected (i.e., the case where X and Y are connectedwithout another element or another circuit positioned therebetween) areincluded therein. That is, when it is explicitly described that “X and Yare electrically connected”, the description is the same as the casewhere it is explicitly only described that “X and Y are connected”.

Even when independent components are electrically connected to eachother in a circuit diagram, one component has functions of a pluralityof components in some cases. For example, when part of a wiring alsofunctions as an electrode, one conductive film functions as the wiringand the electrode. Thus, “electrical connection” in this specificationincludes in its category such a case where one conductive film hasfunctions of a plurality of components.

Note that for example, the case where a source (or a first terminal orthe like) of a transistor is electrically connected to X through (or notthrough) Z1 and a drain (or a second terminal or the like) of thetransistor is electrically connected to Y through (or not through) Z2,or the case where a source (or a first terminal or the like) of atransistor is directly connected to one part of Z1 and another part ofZ1 is directly connected to X while a drain (or a second terminal or thelike) of the transistor is directly connected to one part of Z2 andanother part of Z2 is directly connected to Y, can be expressed by usingany of the following expressions.

The expressions include, for example, “X, Y, a source (or a firstterminal or the like) of a transistor, and a drain (or a second terminalor the like) of the transistor are electrically connected to each other,and X, the source (or the first terminal or the like) of the transistor,the drain (or the second terminal or the like) of the transistor, and Yare electrically connected to each other in this order”, “a source (or afirst terminal or the like) of a transistor is electrically connected toX, a drain (or a second terminal or the like) of the transistor iselectrically connected to Y, and X, the source (or the first terminal orthe like) of the transistor, the drain (or the second terminal or thelike) of the transistor, and Y are electrically connected to each otherin this order”, and “X is electrically connected to Y through a source(or a first terminal or the like) and a drain (or a second terminal orthe like) of a transistor, and X, the source (or the first terminal orthe like) of the transistor, the drain (or the second terminal or thelike) of the transistor, and Y are provided to be connected in thisorder”. When the connection order in a circuit configuration is definedby an expression similar to the above examples, a source (or a firstterminal or the like) and a drain (or a second terminal or the like) ofa transistor can be distinguished from each other to specify thetechnical scope. Note that these expressions are examples and there isno limitation on the expressions. Here, X, Y, Z1, and Z2 each denote anobject (e.g., a device, an element, a circuit, a wiring, an electrode, aterminal, a conductive film, or a layer).

Note that the terms “film” and “layer” can be interchanged with eachother depending on the case or circumstances. For example, the term“conductive layer” can be changed into the term “conductive film” insome cases. In addition, the term “insulating film” can be changed intothe term “insulating layer” in some cases.

Embodiment 1

In this embodiment, a display device of one embodiment of the presentinvention will be described with reference to the drawings.

The “display device” in this specification means an image display deviceor a light source (including a lighting device). Further, the displaydevice includes any of the following modules in its category: a moduleincluding a connector such as a flexible printed circuit (FPC), or tapecarrier package (TCP); a module including TCP which is provided with aprinted wiring board at the end thereof; and a module including a drivercircuit which is directly mounted on a display element by a chip onglass (COG) method.

The display device that is one embodiment of the present invention hasflexibility (flexible display device). Note that “flexible device” meansthat a device can be bent or warped.

FIG. 1A is a schematic diagram illustrating a cross section of a displaydevice of one embodiment of the present invention. The display deviceillustrated in FIG. 1A includes a first substrate 41, a second substrate42, and an element layer 50. The element layer 50 is provided betweenthe first substrate 41 and the second substrate 42.

The first substrate 41 and the second substrate 42 have flexibility. Itis preferable that the first substrate 41 and the second substrate 42 beformed using the same material and have the same thickness to prevent awarp due to thermal expansion or the like. Note that the two substratesand the element layer 50 can be bonded using bonding layers that are notillustrated.

The element layer 50 includes a display element, a distortion sensorelement, a first circuit electrically connected to the display element,and a second circuit electrically connected to the distortion sensorelement. The display device of one embodiment of the present inventionincludes the distortion sensor element, thereby sensing distortion ofthe first substrate 41 and/or the second substrate 42. As a result, thedisplay device self-detects the shape of a display portion and canperform display suitable for the shape.

As the display element, typically, an organic EL element can be used.Instead of an organic EL element, an inorganic EL element can be used. Aliquid crystal element can also be used. For example, a reflectivedisplay device can be provided by combination of a liquid crystalelement and a reflective electrode. A transmissive display device can beprovided by combination of a liquid crystal element and a thin lightsource such as an organic EL element. A semi-transmissive display devicecan be provided by combination of a liquid crystal element, a reflectiveelectrode, and a thin light source.

As the distortion sensor element, typically, a metal thin film resistorcan be used. The amount of distortion in the vicinity of the regionwhere the metal thin film resistor is provided can be measured on thebasis of the amount of change in the resistance of the metal thin filmresistor. As the distortion sensor element, a piezoelectric element canalso be used. As the piezoelectric element, an element including apiezoelectric substance such as barium titanate, lead zirconatetitanate, or zinc oxide can be used.

The first circuit electrically connected to the display element canfunction as a pixel circuit. When the display element is an organic ELelement, a circuit configuration including two transistors and onecapacitor can be employed, for example. When the display element is aliquid crystal element, a circuit configuration including one transistorand one capacitor can be employed.

The second circuit electrically connected to the distortion sensorelement has a function of reading the amount of change in the resistanceof the distortion sensor element. The second circuit can include, forexample, two or three transistors.

The display device of one embodiment of the present invention may have astructure illustrated in FIG. 1B. The display device illustrated in FIG.1B includes the first substrate 41, the second substrate 42, and a firstelement layer 51, and a second element layer 52. The first and secondelement layers 51 and 52 are provided between the first substrate 41 andthe second substrate 42.

The first element layer 51 includes a display element and a firstcircuit electrically connected to the display element. The secondelement layer 52 includes a distortion sensor element. A second circuit,which has a function of reading the amount of change in the resistancefrom the distortion sensor element, can be provided outside the displaydevice. The second circuit may be included in the second element layer52. The second circuit may be included in the first element layer 51.

FIG. 2A is an example of a top view of a pixel portion 80 and drivercircuits in the display device of one embodiment of the presentinvention.

The pixel portion 80 includes pixels 81 arranged in matrix anddistortion sensor elements 82. The pixel 81 includes the above displayelement and first circuit. The first circuit is electrically connectedto a circuit 71 and a circuit 72. The circuit 71 can function as asignal line driver circuit (source driver), for example. The circuit 72can function as a scan line driver circuit (gate driver), for example.

The distortion sensor element 82 is provided so as to be included in anyof the pixels 81 or to overlap with any of the pixels 81. For example,as shown in FIGS. 2A and 2B, one distortion sensor element 82 can beprovided for every four pixels adjacent to one another horizontally andvertically. Because the pitch of the pixels 81 is extremely small,distortion of the pixel portion 80 can be efficiently sensed when thedistortion sensor element 82 is provided for every plurality of thepixels 81. It is needless to say that the number of the distortionsensors 82 may be greater than or equal to the total number of thepixels 81.

The above-described second circuit can be included in the pixel 81, canbe provided to overlap with the pixel 81, or can be externally provided.A circuit 73 and a circuit 74 are a circuit selecting the distortionsensor element 82 and a circuit for reading a signal, respectively. Thesecond circuit can also be included in any of the circuit 73 and thecircuit 74.

FIG. 2B illustrates only the distortion sensor element 82 provided inthe pixel portion 80. The left right arrows represent the distortionsensor elements that are arranged to be able to sense distortion in thehorizontal direction, and the up down arrows represent the distortionsensor elements that are arranged to be able to sense distortion in thevertical direction. The metal thin film resistor senses distortion(bend) in a major-axis direction; thus, by being arranged such that ametal thin film resistor in facing in one direction and a metal thinfilm resistor facing in another direction are alternately arranged asillustrated in FIG. 2B, the metal thin film resistors can accuratelyread data on change in shape in both the horizontal direction and thevertical direction. When change in only one of the horizontal directionand the vertical direction needs to be read out, the distortion sensorelements 82 are arranged only in the corresponding direction. Inaddition, the distortion sensor elements facing in the directioncorresponding to the horizontal direction may overlap with those facingin the direction corresponding to the vertical direction.

FIG. 3A is an example of a cross-sectional view of a display device thatincludes an organic EL element as a display element. Note that FIG. 3Aillustrates part of typical structures in a region 302 including adisplay element of the pixel 81, a region 303 including the distortionsensor element 82, a region 304 including the circuit 71, and a flexibleprinted circuit (FPC) connection region 305. FIG. 3B is a top view ofthe distortion sensor element 82, with which change in shape in thedirection indicated by the up down arrow can be sensed. Note thatalthough not illustrated, regions including the circuits 72 to 74 canhave a structure similar to that of the region 304.

In the display device illustrated in FIG. 3A, which is one example ofthe display device illustrated in FIG. 1A, the first substrate 41, aninsulating film 321 a, the element layer 50, an insulating film 321 b,and the second substrate 42 are stacked in this order. Note that bondinglayers or the like that are not illustrated may be provided between thefirst substrate 41 and the insulating film 321 a and between theinsulating film 321 b and the second substrate 42. Furthermore, a touchsensor may be provided.

As the insulating film 321 a and the insulating film 321 b, a singlelayer of a silicon oxide film, a silicon oxynitride film, a siliconnitride film, or a silicon nitride oxide film, or a stacked layerincluding any of the films can be used.

In FIG. 3A, the element layer 50 includes a transistor 350, a transistor352, a transistor 354, the distortion sensor element 82, an insulatingfilm 364, an insulating film 368, a planarization insulating film 370, aconnection electrode 360, a conductive film 372, a conductive film 374,an insulating film 334, a sealing layer 432, a coloring layer 336 (colorfilter), and a light-blocking layer 338 (black matrix). The elementlayer 50 is sealed with the first substrate 41, the second substrate 42,the sealing layer 432, and a sealant 312. Note that there is a casewhere part of the above components is not included or a component otherthan the above components is included in the element layer 50.

The insulating film 364 can be formed using, for example, silicon oxideor silicon oxynitride. The insulating film 364 is preferably formedusing an oxide insulating film containing oxygen in excess of that inthe stoichiometric composition. The insulating film 368 has a functionof blocking oxygen, hydrogen, water, an alkali metal, an alkaline earthmetal, or the like. For example, a nitride insulating film is preferablyused.

The planarization insulating film 370 can be formed using aheat-resistant organic material, such as a polyimide resin, an acrylicresin, a polyimide amide resin, a benzocyclobutene resin, a polyamideresin, or an epoxy resin. Note that the planarization insulating film370 may be formed by stacking a plurality of insulating films formedusing these materials.

In the region 302, the transistor 350 is included in the first circuitand is electrically connected to an organic EL element 480. The organicEL element 480 includes the conductive film 372, an EL layer 446, andthe conductive film 374. The display device illustrated in FIG. 3A iscapable of displaying an image by light emission from the EL layer 446included in the organic EL element 480.

An insulating film 430 is provided over the conductive film 372 over theplanarization insulating film 370. The insulating film 430 covers partof the conductive film 372. A conductive film with high properties ofreflecting light emitted from the EL layer 446 is used for theconductive film 372, and a conductive film with high properties oftransmitting the light is used for the conductive film 374, whereby theorganic EL element 480 can have a top emission structure. Alternatively,a conductive film with high properties of transmitting the light is usedfor the conductive film 372, and a conductive film with high propertiesof reflecting the light is used for the conductive film 374, whereby theorganic EL element 480 can have a bottom emission structure. Furtheralternatively, a conductive film with high properties of transmittingthe light is used for both the conductive film 372 and the conductivefilm 374, whereby a dual emission structure can be obtained.

For the insulating film 430, an organic resin or an inorganic insulatingmaterial can be used, for example. As the organic resin, for example, apolyimide resin, a polyamide resin, an acrylic resin, a siloxane resin,an epoxy resin, or a phenol resin can be used. As the inorganicinsulating material, silicon oxide, or silicon oxynitride can be used,for example.

The coloring layer 336 is provided to overlap with the organic ELelement 480, and the light-blocking layer 338 is provided to overlapwith the insulating film 430. The coloring layer 336 and thelight-blocking layer 338 are covered with the insulating film 334. Aspace between the organic EL element 480 and the insulating film 334 isfilled with the sealing layer 432.

For the sealing layer 432, a solid sealing material with flexibility canbe used. For example, a glass material such as a glass frit, or a resinmaterial such as a resin, which is curable at room temperature (e.g., atwo-component-mixture-type resin), a light curable resin, or athermosetting resin can be used.

Although a structure with the coloring layer 336 is described as thedisplay device in FIG. 3A, the structure is not limited thereto. In thecase where the EL layers 446 with different emission colors areselectively formed, the coloring layer 336 is not necessarily provided.The color of the coloring layer 336 is not limited to three colors of R(red), G (green), and B (blue). For example, four pixels of an R pixel,a G pixel, a B pixel, and a W (white) pixel may be included.Alternatively, a color element may be composed of two colors among R, G,and B as in PenTile layout. The two colors may differ among colorelements. Alternatively, one or more colors of yellow, cyan, magenta,and the like may be added to RGB. Further, the size of a display regionmay be different between respective dots of the color elements.Embodiments of the disclosed invention are not limited to a displaydevice for color display; the disclosed invention can also be applied toa display device for monochrome display.

Each of the first substrate 41 and the second substrate 42 is preferablyformed using a material with high toughness. Thus, a display device withhigh impact resistance that is less likely to be broken can be provided.For example, when an organic resin substrate is used as the firstsubstrate 41 and the second substrate 42, the display device can belightweight and unlikely to broken as compared to the case where a glasssubstrate is used as the substrate.

For the first substrate 41 and the second substrate 42, for example, amaterial selected from the following can be used: glass which is thinenough to have flexibility, polyester resins such as polyethyleneterephthalate (PET) and polyethylene naphthalate (PEN), apolyacrylonitrile resin, a polyimide resin, a polymethyl methacrylateresin, a polycarbonate (PC) resin, a polyethersulfone (PES) resin, apolyamide resin, a cycloolefin resin, a polystyrene resin, a polyamideimide resin, a polyvinyl chloride resin, and a polyether etherketone(PEEK) resin. In particular, a material whose thermal expansioncoefficient is low is preferred, and for example, a polyamide imideresin, a polyimide resin, or PET is preferably used. A substrate inwhich a glass fiber is impregnated with an organic resin or a substratewhose thermal expansion coefficient is reduced by mixing an organicresin with an inorganic filler can also be used.

In the region 303, the transistor 352 can be included in the secondcircuit. Electrodes of the distortion sensor element 82 are electricallyconnected to the respective wirings. One of the wirings is electricallyconnected to a gate electrode of the transistor 352.

In the region 304, the transistor 354 can be included in the circuit 71.Although the transistor 350, the transistor 352, and the transistor 354have the same size (e.g., channel length and channel width) in thedrawing, one embodiment of the present invention is not limited thereto.The transistors can have their appropriate sizes. The same applies tothe circuits 72 to 74.

Furthermore, although the circuit 71 is provided in the region 304 inFIG. 3A, the circuit may be formed by mounting an IC chip by chip onglass (COG) or the like. Alternatively, the circuit may be connected toa TCP or the like. The same applies to the circuits 72 to 74.

The FPC connection region 305 includes the connection electrode 360, ananisotropic conductive film 380, and an FPC 316. The connectionelectrode 360 can be formed in a step of forming the source electrodelayer and the drain electrode layer of the transistor. The connectionelectrode 360 is electrically connected to a terminal included in theFPC 316 through the anisotropic conductive film 380.

Note that the distortion sensor element 82 senses change in resistancedue to expansion and contraction of the metal thin film; thus, onesurface and the other surface of the metal thin film are preferably incontact with different materials having the respective mechanicalproperties (e.g., elastic modulus, bending strength, a Young's modulus,Poisson's ratio, or hardness) so that the metal thin film can easilyexpand and contract. For example, in the structure in FIGS. 3A and 3B,one surface is in contact with the planarization insulating film 370,and the other surface is in contact with the insulating film 430. Here,since the planarization insulating film 370 and the insulating film 430are formed using materials with different mechanical properties, thesurface on which the metal thin film can expand and contract relativelyeasily is determined Therefore, for example, the metal thin film expandswhen the shape is changed to be convex, and the metal thin filmcontracts when the shape is changed to be concave. Accordingly, thedirection of change in shape can be sensed on the basis of theresistance when the metal thin film expands and the resistance when themetal thin film contracts.

The display device of one embodiment of the present invention may have astructure illustrated in the cross-sectional view in FIG. 4. The displaydevice illustrated in FIG. 4 is an example of the display device in FIG.1B and includes a region 306 in which the region 303 and the region 304of the display device illustrated in FIG. 3A are stacked.

In a lower layer of the region 306, a transistor 354 a and a transistor354 b are provided and these transistors can be included in any of thecircuits 71 to 74.

In an upper layer of the region 306, which is provided over the lowerlayer with an insulating layer 366 positioned therebetween, thedistortion sensor element 82, the transistor 352, and a planarizationinsulating film 371 are provided. The planarization insulating film 371can be formed using a material similar to that for the planarizationinsulating film 370.

In the region 302, the distortion sensor element 82 and the transistor352 may be formed on a surface opposite to the surface through whichlight from the organic EL element 480 is emitted. Note that the circuitincluding the transistor 352 may be provided in an external IC chip. Inother words, a structure in which the transistor 352 is not provided inthe upper layer of the region 306 may be employed.

In the structures illustrated in FIGS. 3A and 3B and FIG. 4, two or moredistortion sensor elements may be provided at different heights (in thethickness direction) between the first substrate 41 and the secondsubstrate 42. The distortion sensor element may be provided over thefirst substrate 41, the second substrate 42, or both the first substrate41 and the second substrate 42.

The transistor in the above display device is preferably a transistorwhose channel formation region is provided in an oxide semiconductorlayer.

Since the transistor using an oxide semiconductor layer has highmobility, an area occupied by transistors can be made small, and theaperture ratio can be increased. With use of the transistor, thecircuits 71 to 74 can be formed over the substrate provided with thepixel portion 80. In addition, the transistor has extremely lowoff-state current and can hold a video signal or the like for a longerperiod; thus, the frame frequency can be lowered, and the powerconsumption of the display device can be reduced.

Furthermore, a transistor including an oxide semiconductor layer ispreferably used as the transistor electrically connected to thedistortion sensor element 82. By the use of a transistor with anextremely low off-state current as the transistor, electric charge whichis unnecessarily input and output into and from an output wiring or thelike can be inhibited.

The oxide semiconductor layer preferably includes a c-axis alignedcrystal. In the case where the oxide semiconductor layer including thecrystal is used for a channel formation region of the transistor, acrack or the like is less likely to occur in the oxide semiconductorlayer when the display device 300 is bent, for example. As a result, thereliability can be improved.

Note that the transistor including an oxide semiconductor layer ismerely an example, and a transistor including an amorphous silicon layeror a polycrystalline silicon layer can also be used. Alternatively, atransistor including an organic semiconductor may be used. Examples ofan organic semiconductor include acenes such as tetracene and pentacene,oligothiophene derivatives, phthalocyanines, perylene derivatives,rubrene, Alq₃, TTF-TCNQ, polythiophene (e.g., poly(3-hexylthiophene)(P3HT)), polyacetylene, polyfluorene, polyphenylene vinylene,polypyrrole, polyaniline, anthracene, tetracyanoquinodimethane (TCNQ),and polyparaphenylene vinylene (PPV).

FIG. 5 is an example of a block diagram of a display device of oneembodiment of the present invention. A display device 5000 includes adisplay portion 5001, a distortion sensor portion 5002, a circuit 5010,a circuit 5020, a circuit 5030, and a circuit 5050. Note that astructure may be employed in which components other than the displayportion 5001 and the distortion sensor portion 5002 are not provided inthe display device 5000 and externally provided. To the display device5000, various circuits such as a control circuit, an arithmetic circuit,a power supply circuit, and a memory circuit that are not shown in thedrawing can be connected.

Here, the circuit 5010 can have a function of controlling the displayportion. The circuit 5020 can have a function of image processing. Thecircuit 5030 can have a function of converting an image signal. Thecircuit 5050 can have a function of controlling the distortion sensorportion 5002.

For example, an analog video signal outputted from a video signal outputdevice 5040 such as a camera or an image reproducing device is inputtedto the circuit 5030 to be converted into a digital video signal. Thedigital video signal is transmitted to the display portion 5001 throughthe circuit 5020 and the circuit 5010, so that the display portion 5001displays an image.

The shape of the display portion 5001 having flexibility is sensed inthe distortion sensor portion 5002 and data on the shape is inputted tothe circuit 5020 through the circuit 5050.

The circuit 5020 performs processing related to data on the shape of thedisplay portion. When signals obtained from the distortion sensorportion 5002 are arranged two-dimensionally, data on the shape of thedisplay portion 5001 can be obtained. Note that depending on the usage,data on the shape only in the horizontal direction or the verticaldirection of the display portion 5001 may be obtained. An image signalcorresponding to the shape of the display portion is outputted to thecircuit 5010.

Note that a signal specifying a display mode of an image may be inputtedfrom a control device 5060 to the circuit 5020. The control device 5060can also be operated by a viewer. The control device 5060 has a sensingfunction with respect to a viewer and can control the circuit 5020 suchthat an image with high viewability is automatically displayed towardthe viewer. Note that the control device 5060 may be included in thedisplay device 5000. The control device 5060 can input a signal to thedisplay device 5000 by wireless communication.

In the above manner, the display device of one embodiment of the presentinvention can self-detect the shape of the display portion. Moreover, asuitable image can be displayed in accordance with the shape of thedisplay portion.

An example of a display mode for the display device of one embodiment ofthe present invention at the time when the shape of the display portionis changed is described. Note that in the initial state, the displayportion is substantially flat and performs or is capable of performingimage display as shown in FIG. 6A.

For example, in the case where the display portion is divided into twoby being mountain-folded or valley-folded, an image can be displayed inreduced form on only one display portion, as illustrated in FIG. 6B.Display can be switched from a portrait mode (in FIG. 6B) to a landscapemode (in FIG. 6C). Here, the other display portion, which does notperform display, is in an off state, whereby power consumption can bereduced. Note that the bending position of the display portion and thenumber of divisions formed by bending are not limited.

In the case where an image in the initial state is displayed on thedisplay portion divided into two as described above, an image is viewedas if distorted as illustrated in FIG. 6D when viewed from a specificdirection, resulting in low viewability. However, when an image that ischanged in shape is displayed as illustrated in FIG. 6E, the viewabilityof the image when viewed from the same direction can be improved.

When the display portion is bent to have a curved surface, an image canbe displayed in reduced form in a region of the display portion that canbe easily viewed, as illustrated in FIG. 6F.

In the case where the display portion has a wavy shape as illustrated inFIG. 7A and a viewer views the display portion from the directionindicated by the arrow, display in a region not seen from the positionof the viewer can be turned off, and display can be performed in aregion that can be seen by the viewer. When display is performed in sucha manner, the viewer can view an image with high viewability asillustrated in FIG. 7B. In addition, an image can be changed inaccordance with the shape of the display portion; thus, even when theshape of the display portion is constantly changed, the viewer can viewan image with high viewability.

Note that in the display portion divided into two or more by bending orthe like, a region in which image display is performed, a region inwhich image display is turned off, and a region in which an image ischanged in shape can be set as appropriate. For example, there are amethod in which the region where the above operation is performed is setin advance and a method in which the region where the above operation isperformed is switched by a function using a touch sensor or a distortionsensor or the like. A method in which the region where the aboveoperation is performed is automatically set with the use of a sensorthat senses the position of the viewer can also be used. Note that thesensor corresponds to the control device 5060 in FIG. 5.

The structure described in this embodiment can be used in appropriatecombination with the structure described in any of the otherembodiments.

Embodiment 2

In this embodiment, an example of a method for performing the display inEmbodiment 1, which is described with reference to FIGS. 7A and 7B, withthe use of the display device of one embodiment of the present inventionwill be described.

FIG. 32 illustrates, using the block diagram in FIG. 5, the flow ofprocessing for performing the display in FIGS. 7A and 7B. A flow chartin FIG. 33 shows the flow illustrated in FIG. 32. Note that the flowchart in FIG. 33 mainly illustrates operation in the circuit 5020.

Image data inputted from the video signal output device 5040 to thecircuit 5030 is inputted to the circuit 5020; then, the circuit 5020forms a virtual screen (S101). The virtual screen is regarded as ascreen on which an image that a viewer can see most easily is displayed,and corresponds to, for example, a screen on which an image asillustrated in FIG. 6A is displayed. It can be said that this state isone in which the viewer views an image displayed on a flat screen in thefront.

Next, from the display portion 5001 (which includes the distortionsensor portion 5002) with a given shape, the circuit 5020 extracts dataon the shape through the circuit 5050 and forms a three-dimensionalshape model of the display portion 5001 (S102).

Then, the circuit 5020 extracts positional data of the viewer from thecontrol device 5060. Note that S101, S102, and the extraction of thepositional data of the viewer are not necessarily performed in the aboveorder and may be performed in parallel with one another or may beperformed one by one in no particular order.

Then, the circuit 5020 regards the above three-dimensional shape modelviewed from the viewer as a two-dimensional display portion and assignscoordinates to the two-dimensional display portion (S103).

A portion of the display portion 5001 not seen from the position of theviewer is determined by calculation (S104).

Then, the circuit 5020 converts coordinates of the virtual screen to thecoordinates of the above two-dimensional display portion (S105).

Image data processed in the above manner is transmitted to the displayportion 5001 through the circuit 5010 and display is performed. At thistime, display on the portion of the display portion 5001 not seen fromthe position of the viewer can be turned off (S106).

Next, description is made on processing that is performed when ananticipated change in status (interruption) occurs in a state where, forexample, an image is displayed on the display portion 5001 as a resultof the above-described processing. Here, processing in response tochange in the shape of the display portion 5001, change in the positionof the viewer, and an image change instruction, each of which isinterruption, is described with reference to the flow chart in FIG. 34.

In the flow chart in FIG. 34, the initial state is the state where animage is displayed by the processing shown in the flow chart in FIG. 33.Note that the initial state may be a state where no image is displayed.In this state, the display device 5000 senses the status (S201).

First, whether change in the shape of the display portion 5001, which isinterruption, occurs or not is determined. In the case where the shapeof the display portion 5001 is changed, data on the shape of the displayportion 5001 is extracted and the operation proceeds to a step offorming a new three-dimensional shape model (S202).

In the case where the shape of the display portion 5001 is not changed,whether the position of the viewer is changed or not is determined. Inthe case where the position of the viewer is changed, positional data ofthe viewer is extracted and the three-dimensional shape model isregarded as a new two-dimensional display portion; then, the operationproceeds to a step of assigning coordinates to the two-dimensionaldisplay portion (S203). After the step of S203, the steps of S204, S206,and S207 are performed one by one.

In the case where the position of the viewer is not changed, whether animage change instruction is issued or not is determined. In the casewhere an image change instruction is issued, new image data is acquiredand the operation proceeds to a step of forming a virtual screen (S205).After the step of S205, the steps of S206 and S207 are performed one byone.

When an image change instruction is not issued as interruption, theoperation returns to S201 to deal with the next interruption. Theoperation may be terminated without returning to S201. Note that S201may be performed by the viewer at a given timing or may be performed atregular intervals with the use of a timer or the like. Alternatively,the steps from S201 to S207 may be repeated.

The above three-dimensional shape model can be formed in accordance withthe flow chart in FIG. 35.

First, the control device 5060 or the like is used to sense the positionof the distortion sensor element that is closer to the viewer than anyother distortion sensor elements provided in the distortion sensorportion 5002 overlapping with the display portion 5001 are (S301). Notethat there is no limitation on the kind and position of a sensor tosense the position of the distortion sensor element that is the closestto the viewer. For example, the sensor may be provided to be in contactwith the display portion 5001.

With the use of the position of the distortion sensor element sensed inS301 as an origin (S302), extraction of data is performed in thedistortion sensor elements one by one in order of closeness to theorigin. Note that the distortion sensor element from which data isextracted may be all the distortion sensor elements included in thedisplay device 5000 or may be only the distortion sensor elementpositioned in a specified position.

Then, three-dimensional coordinates are plotted in accordance with thedistance from the origin to the distortion sensor element from whichdata is extracted and data on distortion of the distortion sensorelement (S303). In the above manner, the three-dimensional shape modelcan be formed.

The display device 5000 may have a program in which the steps in theabove-mentioned flow charts are written. Alternatively, the controldevice that controls the display device 5000 may have the program.Further alternatively, the program may be stored in a memory medium.

The structure described in this embodiment can be used in appropriatecombination with the structure described in any of the otherembodiments.

Embodiment 3

In this embodiment, the distortion sensor element and the second circuithaving a function of reading the amount of change in resistance of thedistortion sensor element which are described in Embodiment 1, will bedescribed in more detail. Note that in this embodiment, the secondcircuit electrically connected to the distortion sensor element iscalled a distortion sensor circuit.

FIG. 8A illustrates an example of a distortion sensor circuit thatincludes, as a distortion sensor element, a variable resistor such as ametal thin film resistor. The distortion sensor circuit includes atransistor 501, a transistor 502, a variable resistor 510, and aresistor 520.

One of a source and a drain of the transistor 501 is electricallyconnected to a wiring 540, and the other of the source and the drain iselectrically connected to one of a source and a drain of the transistor502. The other of the source and the drain of the transistor 502 iselectrically connected to a wiring 550, and a gate thereof iselectrically connected to a wiring 530. One terminal of the variableresistor 510 is electrically connected to a wiring 560, and the otherterminal thereof is electrically connected to one terminal of theresistor 520 and a gate of the transistor 501. The other terminal of theresistor 520 is electrically connected to a wiring 570.

Here, the wiring 530 can function as a selection signal line of thedistortion sensor circuit. The wiring 540 can function as a high powersupply potential line. The wiring 550 can function as an output signalline. The wiring 560 can function as a high power supply potential line.The wiring 570 can function as a low power supply potential line. Notethat the wiring 560 may be a low power supply potential line and thewiring 570 may be a high power supply potential line.

Conduction and non-conduction of the transistor 501 are controlled withthe potential of a node ND1, and conduction and non-conduction of thetransistor 502 are controlled with the potential of the wiring 530.

For example, with the assumption that a potential Vpc2 of the wiring 540and the initial potential Vini of the wiring 550 satisfy Vini<Vpc2, whenthe potential of the wiring 530 is at the “H” level and the transistor502 is on, the potential Vout of the wiring 550 depends on whether thetransistor 501 is on or off. In other words, the potential Vout of thewiring 550 depends on the potential V1 of the node ND1, which is thegate potential of the transistor 501.

The potential of the node ND1 depends on the resistance R1 of thevariable resistor 510 and the resistance R2 of the resistor 520. Inother words, the potential V1 of the node ND1 can be expressed by theformula below where Vex1 represents the potential of the wiring 560 andVex2 represents the potential of the wiring 570.

$\begin{matrix}{{V\; 1} = {{\frac{R\; 2}{{R\; 1} + {R\; 2}}{Vex}\; 1} + {\frac{R\; 1}{{R\; 1} + {R\; 2}}{Vex}\; 2}}} & \lbrack {{Formula}\mspace{14mu} 1} \rbrack\end{matrix}$

According to the above formula, V1 decreases when the resistance R1 ofthe variable resistor 510 changes in the positive direction, and V1increases when the resistance R1 of the variable resistor 510 changes inthe negative direction. In the distortion sensor circuit, the potentialcorresponding to V1 is outputted to the wiring 550. Thus, the amount ofdistortion of the variable resistor 510 can be known from the potentialoutputted to the wiring 550.

Note that the distortion sensor circuit of one embodiment of the presentinvention may have a structure illustrated in FIG. 8B. The distortionsensor circuit in FIG. 8B is different from the distortion sensorcircuit in FIG. 8A in that it includes a transistor 503. One of a sourceand a drain of the transistor 503 is electrically connected to oneterminal of the variable resistor 510, and the other of the source andthe drain is electrically connected to the wiring 560. A gate of thetransistor 503 is electrically connected to the wiring 530.

The transistor 503 is on only when the potential of the wiring 530 is atthe “H” level, i.e., when the distortion sensor circuit is selected.Therefore, the transistor 503 is off when the potential of the wiring530 is at the “L” level, whereby current unnecessarily flowing betweenthe wiring 560 and the wiring 570 can be suppressed.

FIG. 9 illustrates an example of a circuit in which a distortion sensorcircuit portion 91, which is similar to the circuit in FIG. 8A, and apixel circuit portion 92 including an organic EL element are combined.The pixel circuit portion 92 includes a transistor 504, a transistor505, a capacitor 610, and an organic EL element 620.

One of a source and a drain of the transistor 504 is electricallyconnected to a wiring 580, and the other of the source and the drain iselectrically connected to a gate of the transistor 505 and one terminalof the capacitor 610. A gate of the transistor 504 is electricallyconnected to a wiring 590. The other terminal of the capacitor 610 andone of a source and a drain of the transistor 505 are electricallyconnected to the wiring 560. The other of the source and the drain ofthe transistor 505 is electrically connected to one terminal of theorganic EL element 620, and the other terminal of the organic EL element620 is electrically connected to the wiring 570.

In the circuit illustrated in FIG. 9, the other terminal of the organicEL element 620 and the other terminal of the resistor 520 can beelectrically connected to each other.

Here, the wiring 580 can function as a signal line inputting an imagesignal to the pixel circuit portion 92. The wiring 590 can function as aselection signal line of the pixel circuit portion 92.

The transistor 504 is turned on when the potential of the wiring 590 isset at the “H” level, whereby data corresponding to the potential of thewiring 580 can be written into the node ND2. When the potential of thewiring 590 is set at the “L” level, the data in the node ND2 can bestored.

Conduction and non-conduction of the transistor 505 is controlled withthe potential of the node ND2. Accordingly, whether the organic ELelement 620 emits light or not can be controlled with the potential ofthe node ND2.

Note that the circuit may have a structure as illustrated in FIG. 10where the distortion sensor circuit portion 91, which is similar to thecircuit in FIG. 8B, and the pixel circuit portion 92 including theorganic EL element are combined. The other terminal of the capacitor610, one of the source and the drain of the transistor 505, and theother of the source and the drain of the transistor 503 can beelectrically connected to one another.

Although one pixel circuit portion 92 and one distortion sensor circuitportion 91 are combined in the circuits illustrated in FIGS. 9 and 10,the plurality of pixel circuit portions 92 and one distortion sensorcircuit portion 91 can be combined as illustrated in FIG. 11. Note thatalthough four pixel circuit portions (pixel circuit portions 92 a to 92d) are shown in FIG. 11, one embodiment of the present invention is notlimited to this structure and two or more pixel circuit portions and onedistortion sensor circuit portion 91 can be combined. Note that asillustrated in FIG. 12, the distortion sensor circuit portion 91 mayinclude the transistor 503.

Note that the wiring 550 can be provided with a circuit having a readingfunction as illustrated in FIG. 13. The wiring 550 is connected to aselector 630, and a selected signal is inputted to a gate of atransistor 640. Here, a transistor 650 is a switch for resetting thegate potential of the transistor 640 to a potential supplied from awiring 545. A signal outputted from the transistor 640 can be outputtedas digital data through an amplifier 660 and an analog-digital converter670. The wiring 545 can function as a low power supply potential line.Note that the wiring 540 may be a low power supply potential line andthe wiring 545 may be a high power supply potential line.

Although the pixel circuit portion 92 includes the organic EL element620 in the above examples, the pixel circuit portion 92 may include aliquid crystal element 625 as illustrated in FIGS. 14 and 15. It isneedless to say that the transistor 503 may be included in the circuitsillustrated in FIGS. 14 and 15 as in the above-described circuits.

The structure described in this embodiment can be used in appropriatecombination with the structure described in any of the otherembodiments.

Embodiment 4

In this embodiment, a transistor that can be used for a display deviceof one embodiment of the present invention and a material included inthe transistor will be described. The transistor described in thisembodiment can be used for the transistors 350, 352, 354, 501, 502, 503,504, 505, and the like described in the above embodiment.

FIG. 16A is a cross-sectional view of an example of a transistor thatcan be used in a display device of one embodiment of the presentinvention. The transistor includes an insulating film 915 over asubstrate 900, a gate electrode layer 920, a gate insulating film 930 inwhich an insulating film 931 and an insulating film 932 are stacked inthis order, an oxide semiconductor layer 940, and a source electrodelayer 950 and a drain electrode layer 960 in contact with part of theoxide semiconductor layer 940. In addition, an insulating film 980 andan insulating film 990 may be formed over the gate insulating film 930,the oxide semiconductor layer 940, the source electrode layer 950, andthe drain electrode layer 960.

The transistor of one embodiment of the present invention may include,as illustrated in FIG. 16B, a conductive film 921 that overlaps with thegate electrode layer 920 and the oxide semiconductor layer 940 and isover the insulating film 990. When the conductive film 921 is used as asecond gate electrode layer (back gate), the on-state current can beincreased and the threshold voltage can be controlled. To increase theon-state current, for example, the gate electrode layer 920 and theconductive film 921 are set to have the same potential, and thetransistor is driven as a dual-gate transistor. Further, to control thethreshold voltage, a fixed potential that is different from a potentialof the gate electrode layer 920 is supplied to the conductive film 921.

The transistor of one embodiment of the present invention may have achannel-protective bottom-gate structure as illustrated in FIGS. 17A and17B. In this structure, an insulating film 933 has a function ofprotecting a channel region. Thus, the insulating film 933 may beprovided only in a region overlapping with the channel region orprovided in not only the region but also a region other than the regionas illustrated in FIGS. 17A and 17B.

The transistor of one embodiment of the present invention may have aself-aligned top-gate structure as illustrated in FIGS. 18A and 18B. Inthe structure in FIG. 18A, a source region 951 and a drain region 961can be formed in the following manner oxygen vacancies are generated bymaking the source electrode layer 950 and the drain electrode layer 960be in contact with the oxide semiconductor layer 940; and the oxidesemiconductor layer 940 is doped with impurities such as boron,phosphorus, or argon using the gate electrode layer 920 as a mask. Inthe structure in FIG. 18B, the source region 951 and the drain region961 can be formed, instead of using the doping method, in the followingmanner: an insulating film 975 containing hydrogen, such as a siliconnitride film, is formed to be in contact with part of the oxidesemiconductor layer 940 and the hydrogen is diffused to the part of theoxide semiconductor layer 940.

The transistor of one embodiment of the present invention may have aself-aligned top-gate structure as illustrated in FIG. 19A. In thestructure in FIG. 19A, the source region 951 and the drain region 961can be formed in the following manner: oxygen vacancies are generated bymaking the source electrode layer 950 and the drain electrode layer 960be in contact with the oxide semiconductor layer 940; and the oxidesemiconductor layer 940 is doped with impurities such as boron,phosphorus, or argon using the gate insulating film 930 as a mask. Inthe structure in FIG. 19A, the source electrode layer 950, the drainelectrode layer 960, and the gate electrode layer 920 can be aimed inone process.

The transistor of one embodiment of the present invention may have aself-aligned top-gate structure as illustrated in FIG. 19B. In thestructure in FIG. 19B, the source region 951 and the drain region 961can be formed by, besides the doping with impurities such as boron,phosphorus, or argon using the gate insulating film 930 as a mask,diffusion of hydrogen from the insulating film 975 such as a siliconnitride film, which contains hydrogen and is in contact with part of theoxide semiconductor layer 940, to the part of the oxide semiconductorlayer 940. In the structure, the source region 951 and the drain region961 can have lower resistance. Alternatively, a structure in whichdoping with the impurities is not performed or a structure without theinsulating film 975 can be formed.

The transistor of one embodiment of the present invention may include aconductive film 921 overlapping with the oxide semiconductor layer 940with the insulating film 915 interposed therebetween as illustrated inFIGS. 20A and 20B. Although FIGS. 20A and 20B illustrate examples wherethe conductive film 921 is provided in the transistors illustrated inFIGS. 18A and 18B, the conductive film 921 can be provided in thetransistors illustrated in FIGS. 19A and 19B.

In the display device of one embodiment of the present invention, anoxide semiconductor can be used in an active layer as described above.The transistor using an oxide semiconductor layer has a higher mobilitythan a transistor using amorphous silicon, and is thus easily reduced insize, resulting in a reduction in the size of a pixel. The transistorusing an oxide semiconductor layer enables a flexible display device tohave high reliability. Note that one embodiment of the present inventionis not limited thereto. An active layer may include a semiconductorother than an oxide semiconductor depending on the case or condition.

Note that in the cross-sectional structures of the transistorsillustrated in FIGS. 16A and 16B and FIGS. 17A and 17B, the width of thegate electrode layer 920 is preferably larger than that of the oxidesemiconductor layer 940. In the display device having a backlight, thegate electrode layer functions as a light-blocking layer, and adeterioration of electrical characteristics, caused by irradiation ofthe oxide semiconductor layer 940 with light, can be suppressed. In adisplay device including an organic EL element or the like, a gateelectrode layer in a top-gate transistor can function as alight-blocking layer.

Next, the components of the transistor of one embodiment of the presentinvention will be described in detail.

The substrate 900 can be formed using a material that can be used forthe first substrate 41 and the second substrate 42 described inEmbodiment 1. Note that the substrate 900 corresponds to the firstsubstrate 41 in Embodiment 1.

As the insulating film 915, for example, a single layer of a siliconoxide film, a silicon oxynitride film, a silicon nitride film, or asilicon nitride oxide film, or a stacked layer including any of theabove films can be used. The insulating film 915 corresponds to theinsulating film 321 a in Embodiment 1.

The gate electrode layer 920 and the conductive film 921 can be formedusing a metal element selected from chromium (Cr), copper (Cu), aluminum(Al), gold (Au), silver (Ag), zinc (Zn), molybdenum (Mo), tantalum (Ta),titanium (Ti), tungsten (W), manganese (Mn), nickel (Ni), iron (Fe), andcobalt (Co), an alloy including the above metal element, an alloy inwhich any of the above metal elements are combined, or the like.Furthermore, the gate electrode layer 920 may have a single-layerstructure or a stacked structure of two or more layers.

Alternatively, the gate electrode layer 920 and the conductive film 921can be formed using a light-transmitting conductive material such asindium tin oxide, indium oxide containing tungsten oxide, indium zincoxide containing tungsten oxide, indium oxide containing titanium oxide,indium tin oxide containing titanium oxide, indium zinc oxide, indiumtin oxide to which silicon oxide is added, or graphene. A layeredstructure formed using the above light-transmitting conductive materialand the above metal element can also be employed.

Further, an In—Ga—Zn-based oxynitride semiconductor film, an In—Sn-basedoxynitride semiconductor film, an In—Ga-based oxynitride semiconductorfilm, an In—Zn-based oxynitride semiconductor film, a Sn-basedoxynitride semiconductor film, an In-based oxynitride semiconductorfilm, a film of metal nitride (such as InN or ZnN), or the like may beprovided between the gate electrode layer 920 and the insulating film932.

As each of the insulating films 931 and 932 functioning as the gateinsulating film 930, an insulating layer including at least one of thefollowing films formed by a plasma enhanced chemical vapor deposition(PECVD) method, a sputtering method, or the like can be used: a siliconoxide film, a silicon oxynitride film, a silicon nitride oxide film, asilicon nitride film, an aluminum oxide film, a hafnium oxide film, anyttrium oxide film, a zirconium oxide film, a gallium oxide film, atantalum oxide film, a magnesium oxide film, a lanthanum oxide film, acerium oxide film, and a neodymium oxide film. Note that instead of astacked structure of the insulating films 931 and 932, the gateinsulating film 930 may be an insulating film of a single layer formedusing a material selected from the above or an insulating film of threeor more layers.

Note that the insulating film 932 that is in contact with the oxidesemiconductor layer 940 functioning as a channel formation region of thetransistor is preferably an oxide insulating film and preferably has aregion (oxygen-excess region) containing oxygen in excess of thestoichiometric composition. In other words, the insulating film 932 isan insulating film from which oxygen can be released. In order toprovide the oxygen-excess region in the insulating film 932, theinsulating film 932 is formed in an oxygen atmosphere, for example.Alternatively, oxygen may be introduced into the deposited insulatingfilm 932 to provide the oxygen-excess region therein. Oxygen can beintroduced by an ion implantation method, an ion doping method, a plasmaimmersion ion implantation method, plasma treatment, or the like.

In the case where hafnium oxide is used for the insulating films 931 and932, the following effect is attained. Hafnium oxide has higherdielectric constant than silicon oxide and silicon oxynitride.Therefore, when hafnium oxide is used, a thickness can be made largerthan when silicon oxide is used; thus, leakage current due to tunnelcurrent can be low.

In this embodiment, a silicon nitride film is formed as the insulatingfilm 931, and a silicon oxide film is formed as the insulating film 932.A silicon nitride film has a higher dielectric constant than a siliconoxide film and needs a larger thickness for capacitance equivalent tothat of the silicon oxide. Thus, when a silicon nitride film is used forthe gate insulating film 930 of the transistor, the physical thicknessof the insulating film can be increased. From the above, theelectrostatic breakdown of the transistor can be prevented by improvingthe withstand voltage of the transistor.

The oxide semiconductor layer 940 is typically faulted using an In—Gaoxide, an In—Zn oxide, or an In-M-Zn oxide (M is Ti, Ga, Y, Zr, La, Ce,Nd, Sn, or Hf). In particular, an In-M-Zn oxide (M is Ti, Ga, Y, Zr, La,Ce, Nd, Sn, or Hf) is preferably used for the oxide semiconductor layer940.

In the case where the oxide semiconductor layer 940 is an In-M-Zn oxide(M is Ti, Ga, Y, Zr, La, Ce, Nd, Sn, or Hf), it is preferable that theatomic ratio of metal elements of a sputtering target used for forming afilm of the In-M-Zn oxide satisfy In≥M and Zn≥M. The sputtering targetis preferably polycrystalline. As the atomic ratio of metal elements ofsuch a sputtering target, In:M:Zn=1:1:1, In:M:Zn=5:5:6, In:M:Zn=3:1:2,In:M:Zn=2:1:3, and the like are preferable. Note that the atomic ratioof metal elements in the formed oxide semiconductor layer 940 variesfrom the above atomic ratio of metal elements of the sputtering targetwithin a range of ±40% as an error.

In the case of using an In-M-Zn oxide for the oxide semiconductor layer940, when Zn and O are eliminated from consideration, the proportion ofIn and the proportion of M are greater than 25 atomic % and less than 75atomic %, respectively, preferably greater than 34 atomic % and lessthan 66 atomic %, respectively.

The energy gap of the oxide semiconductor layer 940 is 2 eV or more,preferably 2.5 eV or more, and more preferably 3 eV or more. In thismanner, the amount of off-state current of a transistor can be reducedby using an oxide semiconductor having a wide energy gap.

The oxide semiconductor layer 940 has a thickness greater than or equalto 3 nm and less than or equal to 200 nm, preferably 3 nm to 100 nm, andfurther preferably 3 nm to 50 nm.

An oxide semiconductor layer with low carrier density is used as theoxide semiconductor layer 940. For example, an oxide semiconductor layerwhose carrier density is lower than or equal to 1×10¹⁷/cm³, preferablylower than or equal to 1×10¹⁵/cm³, further preferably lower than orequal to 1×10¹³/cm³, still further preferably lower than or equal to1×10¹¹/cm³ is used as the oxide semiconductor layer 940.

However, the composition is not limited to those described above, and amaterial having the appropriate composition may be used depending onrequired semiconductor characteristics and electrical characteristics ofthe transistor (e.g., field-effect mobility and threshold voltage).Further, in order to obtain the required semiconductor characteristicsof the transistor, it is preferable that the carrier density, theimpurity concentration, the defect density, the atomic ratio of a metalelement to oxygen, the interatomic distance, the density, and the likeof the oxide semiconductor layer 940 be set to appropriate values.

Further, in the oxide semiconductor layer, hydrogen, nitrogen, carbon,silicon, and metal elements except for main components are impurities.For example, hydrogen and nitrogen form donor levels to increase thecarrier density. Silicon forms impurity states in the oxidesemiconductor layer. The impurity state becomes a trap, which mightdeteriorate the electrical characteristics of the transistor. It ispreferable to reduce the concentration of the impurities in the oxidesemiconductor layer and at interfaces with other layers.

Note that stable electrical characteristics can be effectively impartedto a transistor in which an oxide semiconductor layer serves as achannel by reducing the concentration of impurities in the oxidesemiconductor layer to make the oxide semiconductor layer intrinsic orsubstantially intrinsic. The term “substantially intrinsic” refers tothe state where an oxide semiconductor layer has a carrier density lowerthan 1×10¹⁷/cm³, preferably lower than 1×10¹⁵/cm³, further preferablylower than 1×10¹³/cm³.

In order to make the oxide semiconductor layer intrinsic orsubstantially intrinsic, in SIMS (secondary ion mass spectrometry), forexample, the concentration of silicon at a certain depth of the oxidesemiconductor layer or in a region of the oxide semiconductor layer islower than 1×10¹⁹ atoms/cm³, preferably lower than 5×10¹⁸ atoms/cm³,more preferably lower than 1×10¹⁸ atoms/cm³. Further, the concentrationof hydrogen at a certain depth of the oxide semiconductor layer or in aregion of the oxide semiconductor layer is lower than or equal to 2×10²⁰atoms/cm³, preferably lower than or equal to 5×10¹⁹ atoms/cm³, furtherpreferably lower than or equal to 1×10¹⁹ atoms/cm³, still furtherpreferably lower than or equal to 5×10¹⁸ atoms/cm³. Further, theconcentration of nitrogen at a certain depth of the oxide semiconductorlayer or in a region of the oxide semiconductor layer is lower than5×10¹⁹ atoms/cm³, preferably lower than or equal to 5×10¹⁸ atoms/cm³,further preferably lower than or equal to 1×10¹⁸ atoms/cm³, stillfurther preferably lower than or equal to 5×10¹⁷ atoms/cm³.

In the case where the oxide semiconductor layer includes crystals, highconcentration of silicon or carbon might reduce the crystallinity of theoxide semiconductor layer. In order not to lower the crystallinity ofthe oxide semiconductor layer, for example, the concentration of siliconat a certain depth of the oxide semiconductor layer or in a region ofthe oxide semiconductor layer is lower than 1×10¹⁹ atoms/cm³, preferablylower than 5×10¹⁸ atoms/cm³, further preferably lower than 1×10¹⁸atoms/cm³. Further, the concentration of carbon at a certain depth ofthe oxide semiconductor layer or in a region of the oxide semiconductorlayer is lower than 1×10¹⁹ atoms/cm³, preferably lower than 5×10¹⁸atoms/cm³, further preferably lower than 1×10¹⁸ atoms/cm³, for example.

Various experiments can prove low off-state current of a transistorincluding a highly purified oxide semiconductor layer for a channelformation region. For example, even when an element has a channel widthof 1×10⁶ μm and a channel length of 10 μm, off-state current can be lessthan or equal to the measurement limit of a semiconductor parameteranalyzer, i.e., less than or equal to 1×10⁻¹³ A, at voltage (drainvoltage) between the source electrode and the drain electrode of from 1V to 10 V. In this case, it can be seen that the off-state currentnormalized on the channel width of the transistor is lower than or equalto 100 zA/μm. In addition, a capacitor and a transistor are connected toeach other and the off-state current is measured with a circuit in whichcharge flowing into or from the capacitor is controlled by thetransistor. In the measurement, a highly purified oxide semiconductorlayer is used for a channel formation region of the transistor, and theoff-state current of the transistor is measured by a change in theamount of electric charge of the capacitor per unit time. As a result,it is found that in the case where the voltage between the sourceelectrode and the drain electrode of the transistor is 3 V, loweroff-state current of several tens of yoctoamperes per micrometer (yA/μm)can be obtained. Accordingly, the off-state current of the transistorincluding a channel formation region formed of the highly purified oxidesemiconductor layer is considerably lower than that of a transistorincluding silicon having crystallinity.

For the source electrode layer 950 and the drain electrode layer 960, aconductive film having properties of extracting oxygen from the oxidesemiconductor layer is preferably used. For example, Al, Cr, Cu, Ta, Ti,Mo, W, Ni, Mn, Nd, or Sc can be used. An alloy or a conductive nitrideof any of these materials can also be used. A stack including aplurality of materials selected from these materials, alloys of thesematerials, and conductive nitrides of these materials can also be used.Typically, it is preferable to use Ti, which is particularly easilybonded to oxygen, or W, which has a high melting point and thus allowssubsequent process temperatures to be relatively high. Alternatively, Cuor a Cu—X alloy (X indicates Mn, Ni, Cr, Fe, Co, Mo, Ta, or Ti), whichhas low resistance may be used. Further alternatively, a stacked layerincluding any of the above materials and Cu or a Cu—X alloy may be used.

In the case of using a Cu—X alloy (X indicates Mn, Ni, Cr, Fe, Co, Mo,Ta, or Ti), a covering film is formed in a region in contact with theoxide semiconductor layer or a region in contact with an insulating filmby heat treatment, in some cases. The covering film includes a compoundcontaining X. Examples of a compound containing X include an oxide of X,an In—X oxide, a Ga—X oxide, an In—Ga—X oxide, and In—Ga—Zn—X oxide.When the covering film is formed, the covering film functions as ablocking film, and Cu in the Cu—X alloy film can be prevented fromentering the oxide semiconductor layer.

By the conductive film capable of extracting oxygen from the oxidesemiconductor layer, oxygen in the oxide semiconductor layer is releasedto form oxygen vacancies in the oxide semiconductor layer. Hydrogenslightly contained in the layer and the oxygen vacancy are bonded toeach other, whereby the region is markedly changed to an n-type region.Accordingly, the n-type regions can serve as a source or a drain regionof the transistor.

The insulating films 980 and 990 each have a function of a protectiveinsulating film. The insulating film 980 is formed using an oxideinsulating film containing oxygen in excess of that in thestoichiometric composition. Part of oxygen is released by heating fromthe oxide insulating film containing oxygen in excess of that in thestoichiometric composition. The oxide insulating film containing oxygenin excess of that in the stoichiometric composition is an oxideinsulating film of which the amount of released oxygen converted intooxygen atoms is greater than or equal to 1.0×10¹⁸ atoms/cm³, preferablygreater than or equal to 3.0×10²⁰ atoms/cm³ in TDS analysis. Note thatthe temperature of the film surface in the TDS analysis is preferablyhigher than or equal to 100° C. and lower than or equal to 700° C., orhigher than or equal to 100° C. and lower than or equal to 500° C.

Silicon oxide, silicon oxynitride, or the like with a thickness greaterthan or equal to 30 nm and less than or equal to 500 nm, preferablygreater than or equal to 50 nm and less than or equal to 400 nm can beused as the insulating film 980.

Further, it is preferable that the amount of defects in the insulatingfilm 980 be small, typically the spin density of a signal which appearsat g=2.001 originating from a dangling bond of silicon, be lower than1.5×10¹⁸ spins/cm³, further preferably lower than or equal to 1×10¹⁸spins/cm³ by ESR measurement. Note that the insulating film 980 isprovided more apart from the oxide semiconductor layer 940 than theinsulating film 970 is; thus, the insulating film 980 may have higherdefect density than the insulating film 970.

The insulating film 990 has a function of blocking oxygen, hydrogen,water, an alkali metal, an alkaline earth metal, or the like. With theinsulating film 990, oxygen diffusion from the oxide semiconductor layer940 to the outside and entry of hydrogen, water, or the like from theoutside to the oxide semiconductor layer 940 can be prevented. As theinsulating film 990, a nitride insulating film can be used, for example.The nitride insulating film is formed using silicon nitride, siliconnitride oxide, aluminum nitride, aluminum nitride oxide, or the like.Note that instead of the nitride insulating film having a blockingeffect against oxygen, hydrogen, water, alkali metal, alkaline earthmetal, and the like, an oxide insulating film having a blocking effectagainst oxygen, hydrogen, water, and the like, may be provided. Theoxide insulating film having a blocking effect against oxygen, hydrogen,water, and the like is formed using aluminum oxide, aluminum oxynitride,gallium oxide, gallium oxynitride, yttrium oxide, yttrium oxynitride,hafnium oxide, hafnium oxynitride, or the like.

Note that the oxide semiconductor layer 940 may have a structure inwhich a plurality of oxide semiconductor layers are stacked. Forexample, as in a transistor illustrated in FIG. 21A, stacked layers of afirst oxide semiconductor layer 941 a and a second oxide semiconductorlayer 941 b may constitute the oxide semiconductor layer 940. The firstoxide semiconductor layer 941 a and the second oxide semiconductor layer941 b may include metal oxides having different atomic ratios. Forexample, one of the oxide semiconductor layers may include one of anoxide containing two kinds of metals, an oxide containing three kinds ofmetals, and an oxide containing four kinds of metals, and the other ofthe oxide semiconductor layers may include another one of the oxidecontaining two kinds of metals, the oxide containing three kinds ofmetals, and the oxide containing four kinds of metals.

Alternatively, the first oxide semiconductor layer 941 a and the secondoxide semiconductor layer 941 b may include the same constituentelements with different atomic ratios. For example, one of the oxidesemiconductor layers may contain In, Ga, and Zn at an atomic ratio of1:1:1, 5:5:6, 3:1:2, or 2:1:3 and the other of the oxide semiconductorlayers may contain In, Ga, and Zn at an atomic ratio of 1:3:2, 1:3:4,1:3:6, 1:4:5, 1:6:4, or 1:9:6. Note that the atomic ratio of each oxidesemiconductor layer varies within a range of ±40% of the above atomicratio as an error.

In the above, one of the oxide semiconductor layers, which is closer tothe gate electrode (the oxide semiconductor layer on the channel side),has an atomic ratio of In≥Ga (in the atomic ratio, In is greater than orequal to Ga); and the other oxide semiconductor layer, which is fartherfrom the gate electrode (the oxide semiconductor layer on the backchannel side), has an atomic ratio of In<Ga. In that case, a transistorwith a high field-effect mobility can be manufactured. On the otherhand, when the oxide semiconductor layer on the channel side has anatomic ratio of In<Ga and the oxide semiconductor layer on the backchannel side has an atomic ratio of In≥Ga (in the atomic ratio, In isgreater than or equal to Ga), the amount of change in the thresholdvoltage of a transistor due to change over time or a reliability testcan be reduced.

Further alternatively, the semiconductor film of the transistor may havea three-layer structure of a first oxide semiconductor layer, a secondoxide semiconductor layer, and a third oxide semiconductor layer. Inthat case, the first to third oxide semiconductor layers may include thesame constituent elements with different atomic ratios. A transistorincluding a three-layer semiconductor film will be described withreference to FIG. 21B and FIGS. 22A and 22B. Note that a structure inwhich a semiconductor film has a stacked structure can be employed forother transistors described in this embodiment.

Each of the transistors illustrated in FIG. 21B and FIGS. 22A and 22Bincludes a third oxide semiconductor layer 942 a, a second oxidesemiconductor layer 942 b, and a first oxide semiconductor layer 942 cwhich are stacked in this order from a gate insulating film side.

The first oxide semiconductor layer 942 c and the third oxidesemiconductor layer 942 a are formed using a material represented byInM_(1x)Zn_(y)O_(z) (x≥1 (x is greater than or equal to 1), y>1, z>0,M₁=Ga, Hf, or the like). The second oxide semiconductor layer 942 b isformed using a material which can be represented by InM_(2x)Zn_(y)O_(z)(x≥1 (x is greater than or equal to 1), y≥x (y is greater than or equalto x), z>0, M₂=Ga, Sn, or the like).

Materials of the first to third oxide semiconductor layers are selectedas appropriate so as to form a well-shaped structure in which theconduction band minimum in the second oxide semiconductor layer 942 b isdeeper from the vacuum level than the conduction band minimum in thefirst and third oxide semiconductor layers 942 c and 942 a.

For example, the first oxide semiconductor layer 942 c and the thirdoxide semiconductor layer 942 a may each have an atomic ratio ofIn:Ga:Zn=1:1:1, 1:3:2, 1:3:4, 1:3:6, 1:4:5, 1:6:4, or 1:9:6; the secondoxide semiconductor layer 942 b may have an atomic ratio ofIn:Ga:Zn=1:1:1, 5:5:6, 3:1:2, or 2:1:3.

Since the first to third oxide semiconductor layers 942 c to 942 ainclude the same constituent elements, the second oxide semiconductorlayer 942 b has few defect states (trap states) at the interface withthe third oxide semiconductor layer 942 a. Specifically, the defectstates (trap states) are fewer than those at the interface between thegate insulating film and the third oxide semiconductor layer 942 a. Forthis reason, when the oxide semiconductor layers are stacked in theabove manner, the amount of change in the threshold voltage of atransistor due to a change over time or a reliability test can bereduced.

Further, a well-shaped structure is preferably formed in which theconduction band minimum in the second oxide semiconductor layer 942 b isdeeper from the vacuum level than the conduction band minimum in thefirst and third oxide semiconductor layers 942 c and 942 a. Whenmaterials of the first to third oxide semiconductor layers are selectedas appropriate, the field-effect mobility of the transistor can beincreased and the amount of change in the threshold voltage of thetransistor due to change over time or a reliability test can be reduced.

Further, the first to third oxide semiconductor layers 942 c to 942 amay be formed using oxide semiconductors having differentcrystallinities. Note that at least the second oxide semiconductor layer942 b that can function as a channel formation region is preferably afilm with crystallinity, further preferably a film in which c-axes arealigned in a direction substantially perpendicular to a surface.

The top-gate transistor illustrated in FIG. 22A or the like preferablyhas any of cross-sectional structures illustrated in FIGS. 23A and 23Bin the channel width direction of a channel formation region. In each ofthe above structures, the gate electrode layer 920 electricallysurrounds the oxide semiconductor layer 940 in the channel widthdirection. This structure increases the on-state current. Such atransistor structure is referred to as a surrounded channel (s-channel)structure.

In the structure including the conductive film 921 as illustrated inFIGS. 20A and 20B, the gate electrode layer 920 and the conductive film921 may be connected to each other through a contact hole, asillustrated in FIG. 23B, so as to have the same potential.

Furthermore, top-view structures of the source electrode layer 950 andthe drain electrode layer 960 of the transistor of one embodiment of thepresent invention can be as illustrated in FIGS. 24A and 24B. Note thatFIGS. 24A and 24B each illustrate only the oxide semiconductor layer940, the source electrode layer 950, and the drain electrode layer 960.As shown in FIG. 24A, the width (W_(SD)) of each of the source electrodelayer 950 and the drain electrode layer 960 may be larger than the width(W_(OS)) of the oxide semiconductor layer 940. Alternatively, W_(SD) maybe smaller than W_(OS) as shown in FIG. 24B. When W_(OS)≥W_(SD) (W_(SD)is less than or equal to W_(OS)) is satisfied, a gate electric field iseasily applied to the entire oxide semiconductor layer 940, so thatelectrical characteristics of the transistor can be improved.

Although the variety of films such as the metal films, the semiconductorfilms, and the inorganic insulating films which are described in thisembodiment typically can be formed by a sputtering method or a plasmaCVD method, such films may be formed by another method, e.g., a thermalCVD method. A metal organic chemical vapor deposition (MOCVD) method oran atomic layer deposition (ALD) method may be employed as an example ofa thermal CVD method.

A thermal CVD method has an advantage that no defect due to plasmadamage is generated since it does not utilize plasma for forming a film.

Deposition by a thermal CVD method may be performed in such a mannerthat a source gas and an oxidizer are supplied to a chamber at a time,the pressure in the chamber is set to an atmospheric pressure or areduced pressure, and reaction is caused in the vicinity of thesubstrate or over the substrate.

Deposition by an ALD method may be performed in such a manner that thepressure in a chamber is set to an atmospheric pressure or a reducedpressure, source gases for reaction are sequentially introduced into thechamber, and then the sequence of the gas introduction is repeated. Forexample, two or more kinds of source gases are sequentially supplied tothe chamber by switching the respective switching valves (also referredto as high-speed valves) such that the source gases are not mixed. Forexample, a first source gas is introduced, an inert gas (e.g., argon ornitrogen) or the like is introduced at the same time as or after theintroduction of the first gas, and then a second source gas isintroduced. Note that in the case where the first source gas and theinert gas are introduced at a time, the inert gas serves as a carriergas, and the inert gas may also be introduced at the same time as theintroduction of the second source gas. Alternatively, the first sourcegas may be exhausted by vacuum evacuation instead of the introduction ofthe inert gas, and then the second source gas may be introduced. Thefirst source gas is adsorbed on the surface of the substrate to form afirst layer; then, the second source gas is introduced to react with thefirst layer; as a result, a second layer is stacked over the firstlayer, so that a thin film is formed. The sequence of the gasintroduction is controlled and repeated plural times until a desiredthickness is obtained, whereby a thin film with excellent step coveragecan be formed. The thickness of the thin film can be adjusted by thenumber of repetition times of the sequence of the gas introduction;therefore, an ALD method makes it possible to adjust a thicknessaccurately and thus is suitable for manufacturing a minute FET.

The variety of films such as the metal film, the semiconductor film, andthe inorganic insulating film which have been disclosed in theembodiments can be formed by a thermal CVD method such as a MOCVD methodor an ALD method. For example, in the case where an In—Ga—Zn oxide filmis formed, trimethylindium, trimethylgallium, and dimethylzinc can beused. Note that the chemical formula of trimethylindium is In(CH₃)₃. Thechemical formula of trimethylgallium is Ga(CH₃)₃. The chemical formulaof dimethylzinc is Zn(CH₃)₂. Without limitation to the abovecombination, triethylgallium (chemical formula: Ga(C₂H₅)₃) can be usedinstead of trimethylgallium and diethylzinc (chemical formula:Zn(C₂H₅)₂) can be used instead of dimethylzinc.

For example, in the case where a hafnium oxide film is formed by adeposition apparatus using an ALD method, two kinds of gases, i.e.,ozone (O₃) as an oxidizer and a source gas which is obtained byvaporizing liquid containing a solvent and a hafnium precursor compound(hafnium alkoxide or hafnium amide such astetrakis(dimethylamide)hafnium (TDMAH)) are used. Note that the chemicalformula of tetrakis(dimethylamide)hafnium is Hf[N(CH₃)₂]₄. Examples ofanother material liquid include tetrakis(ethylmethylamide)hafnium.

For example, in the case where an aluminum oxide film is formed using adeposition apparatus employing ALD, two kinds of gases, e.g., H₂O as anoxidizer and a source gas which is obtained by vaporizing a solvent andliquid containing an aluminum precursor compound (e.g.,trimethylaluminum (TMA)) are used. Note that the chemical formula oftrimethylaluminum is Al(CH₃)₃. Examples of another material liquidinclude tris(dimethylamide)aluminum, triisobutylaluminum, and aluminumtris(2,2,6,6-tetramethyl-3,5-heptanedionate).

For example, in the case where a silicon oxide film is formed by adeposition apparatus using ALD, hexachlorodisilane is adsorbed on asurface where a film is to be formed, chlorine contained in theadsorbate is removed, and radicals of an oxidizing gas (e.g., O₂ ordinitrogen monoxide) are supplied to react with the adsorbate.

For example, in the case where a tungsten film is formed using adeposition apparatus employing ALD, a WF₆ gas and a B₂H₆ gas aresequentially introduced plural times to form an initial tungsten film,and then a WF₆ gas and an H₂ gas are introduced at a time, so that atungsten film is formed. Note that an SiH₄ gas may be used instead of aB₂H₆ gas.

For example, in the case where an oxide semiconductor film, e.g., anIn—Ga—Zn oxide film is formed using a deposition apparatus employingALD, an In(CH₃)₃ gas and an O₃ gas are sequentially introduced pluraltimes to form an In—O layer, a Ga(CH₃)₃ gas and an O₃ gas are introducedat a time to form a GaO layer, and then a Zn(CH₃)₂ gas and an O₃ gas areintroduced at a time to form a ZnO layer. Note that the order of theselayers is not limited to this example. A mixed compound layer such as anIn—Ga—O layer, an In—Zn—O layer, or a Ga—Zn—O layer may be formed bymixing of these gases. Note that although an H₂O gas which is obtainedby bubbling with an inert gas such as Ar may be used instead of an O₃gas, it is preferable to use an O₃ gas, which does not contain H.Further, instead of an In(CH₃)₃ gas, an In(C₂H₅)₃ gas may be used.Instead of a Ga(CH₃)₃ gas, a Ga(C₂H₅)₃ gas may be used. Further, aZn(CH₃)₂ gas may be used.

The structure described in this embodiment can be used in appropriatecombination with the structure described in any of the otherembodiments.

Embodiment 5

A structure of an oxide semiconductor film which can be used for oneembodiment of the present invention is described below.

In this specification, the term “parallel” indicates that the angleformed between two straight lines is greater than or equal to −10° andless than or equal to 10°, and accordingly also includes the case wherethe angle is greater than or equal to −5° and less than or equal to 5°.In addition, the term “perpendicular” indicates that the angle formedbetween two straight lines is greater than or equal to 80° and less thanor equal to 100°, and accordingly also includes the case where the angleis greater than or equal to 85° and less than or equal to 95°.

In this specification, trigonal and rhombohedral crystal systems areincluded in a hexagonal crystal system.

An oxide semiconductor film is classified roughly into a single-crystaloxide semiconductor film and a non-single-crystal oxide semiconductorfilm. The non-single-crystal oxide semiconductor film includes any of ac-axis aligned crystalline oxide semiconductor (CAAC-OS) film, apolycrystalline oxide semiconductor film, a microcrystalline oxidesemiconductor film, an amorphous oxide semiconductor film, and the like.

First, a CAAC-OS film is described.

The CAAC-OS film is one of oxide semiconductor films having a pluralityof c-axis aligned crystal parts.

When observing the CAAC-OS film in a combined analysis image of abright-field image and a diffraction pattern with the use of atransmission electron microscope (TEM) (the combined analysis image isalso referred to as a high-resolution TEM image), a plurality of crystalparts can be found. However, in the high-resolution TEM image, aboundary between crystal parts, that is, a grain boundary is not clearlyobserved. Thus, in the CAAC-OS film, a reduction in electron mobilitydue to the grain boundary is less likely to occur.

According to the high-resolution cross-sectional TEM image of theCAAC-OS film observed in a direction substantially parallel to a samplesurface, metal atoms are arranged in a layered manner in the crystalparts. Each metal atom layer has a morphology reflecting unevenness of asurface over which the CAAC-OS film is formed (hereinafter, a surfaceover which the CAAC-OS film is formed is referred to as a formationsurface) or a top surface of the CAAC-OS film, and is arranged parallelto the formation surface or the top surface of the CAAC-OS film.

On the other hand, according to the high-resolution planar TEM image ofthe CAAC-OS film observed in a direction substantially perpendicular tothe sample surface, metal atoms are arranged in a triangular orhexagonal configuration in the crystal parts. However, there is noregularity of arrangement of metal atoms between different crystalparts.

A CAAC-OS film is subjected to structural analysis with an X-raydiffraction (XRD) apparatus. For example, when the CAAC-OS filmincluding an InGaZnO₄ crystal is analyzed by an out-of-plane method, apeak appears frequently when the diffraction angle (2θ) is around 31°.This peak is derived from the (009) plane of the InGaZnO₄ crystal, whichindicates that crystals in the CAAC-OS film have c-axis alignment, andthat the c-axes are aligned in a direction substantially perpendicularto the formation surface or the top surface of the CAAC-OS film.

Note that when the CAAC-OS film with an InGaZnO₄ crystal is analyzed byan out-of-plane method, a peak of 2θ may also be observed at around 36°,in addition to the peak of 2θ at around 31°. The peak at 2θ of around36° indicates that a crystal having no c-axis alignment is included inpart of the CAAC-OS film. It is preferable that in the CAAC-OS film, apeak of 2θ appear at around 31° and a peak of 2θ not appear at around36°.

The CAAC-OS film is an oxide semiconductor film having low impurityconcentration. The impurity is an element other than the main componentsof the oxide semiconductor film, such as hydrogen, carbon, silicon, or atransition metal element. In particular, an element that has higherbonding strength to oxygen than a metal element included in the oxidesemiconductor film, such as silicon, disturbs the atomic arrangement ofthe oxide semiconductor film by depriving the oxide semiconductor filmof oxygen and causes a decrease in crystallinity. Further, a heavy metalsuch as iron or nickel, argon, carbon dioxide, or the like has a largeatomic radius (molecular radius), and thus disturbs the atomicarrangement of the oxide semiconductor film and causes a decrease incrystallinity when it is contained in the oxide semiconductor film. Notethat the impurity contained in the oxide semiconductor film might serveas a carrier trap or a carrier generation source.

The CAAC-OS film is an oxide semiconductor film having a low density ofdefect states. In some cases, oxygen vacancy in the oxide semiconductorfilm serves as a carrier trap or serves as a carrier generation sourcewhen hydrogen is captured therein.

The state in which impurity concentration is low and density of defectstates is low (the number of oxygen vacancies is small) is referred toas a “highly purified intrinsic” or “substantially highly purifiedintrinsic” state. A highly purified intrinsic or substantially highlypurified intrinsic oxide semiconductor film has few carrier generationsources, and thus can have a low carrier density. Thus, the transistorincluding the oxide semiconductor film rarely has negative thresholdvoltage (is rarely normally on). The highly purified intrinsic orsubstantially highly purified intrinsic oxide semiconductor film has fewcarrier traps. Accordingly, the transistor including the oxidesemiconductor film has little variation in electrical characteristicsand high reliability. Electric charge trapped by the carrier traps inthe oxide semiconductor film takes a long time to be released, and mightbehave like fixed electric charge. Thus, the transistor which includesthe oxide semiconductor film having high impurity concentration and ahigh density of defect states has unstable electrical characteristics insome cases.

With the use of the CAAC-OS film in a transistor, variation in theelectrical characteristics of the transistor due to irradiation withvisible light or ultraviolet light is small.

Next, a microcrystalline oxide semiconductor film is described.

A microcrystalline oxide semiconductor film has a region where a crystalpart is observed in a high-resolution TEM image and a region where acrystal part is not clearly observed in a high-resolution TEM image. Inmost cases, a crystal part in the microcrystalline oxide semiconductorfilm is greater than or equal to 1 nm and less than or equal to 100 nm,or greater than or equal to 1 nm and less than or equal to 10 nm. Amicrocrystal with a size greater than or equal to 1 nm and less than orequal to 10 nm, or a size greater than or equal to 1 nm and less than orequal to 3 nm is specifically referred to as nanocrystal (nc). An oxidesemiconductor film including nanocrystal is referred to as an nc-OS(nanocrystalline oxide semiconductor) film. In a high-resolution TEMimage of the nc-OS film, for example, a grain boundary is not clearlyobserved in some cases.

In the nc-OS film, a microscopic region (for example, a region with asize greater than or equal to 1 nm and less than or equal to 10 nm, inparticular, a region with a size greater than or equal to 1 nm and lessthan or equal to 3 nm) has a periodic atomic order. Note that there isno regularity of crystal orientation between different crystal parts inthe nc-OS film. Thus, the orientation of the whole film is not observed.Accordingly, in some cases, the nc-OS film cannot be distinguished froman amorphous oxide semiconductor depending on an analysis method. Forexample, when the nc-OS film is subjected to structural analysis by anout-of-plane method with an XRD apparatus using an X-ray having adiameter larger than that of a crystal part, a peak which shows acrystal plane does not appear. Furthermore, a diffraction pattern like ahalo pattern appears in a selected-area electron diffraction pattern ofthe nc-OS film which is obtained by using an electron beam having aprobe diameter (e.g., larger than or equal to 50 nm) larger than thediameter of a crystal part. Meanwhile, spots appear in a nanobeamelectron diffraction pattern of the nc-OS film obtained by using anelectron beam having a probe diameter close to, or smaller than thediameter of a crystal part. Further, in a nanobeam electron diffractionpattern of the nc-OS film, regions with high luminance in a circular(ring) pattern are shown in some cases. Also in a nanobeam electrondiffraction pattern of the nc-OS film, a plurality of spots are shown ina ring-like region in some cases.

The nc-OS film is an oxide semiconductor film that has high regularityas compared to an amorphous oxide semiconductor film. Therefore, thenc-OS film has a lower density of defect states than an amorphous oxidesemiconductor film. However, there is no regularity of crystalorientation between different crystal parts in the nc-OS film; hence,the nc-OS film has a higher density of defect states than the CAAC-OSfilm.

Next, an amorphous oxide semiconductor film is described.

The amorphous oxide semiconductor film has disordered atomic arrangementand no crystal part. For example, the amorphous oxide semiconductor filmdoes not have a specific state as in quartz.

In the high-resolution TEM image of the amorphous oxide semiconductorfilm, crystal parts cannot be found.

When the amorphous oxide semiconductor film is subjected to structuralanalysis by an out-of-plane method with an XRD apparatus, a peak whichshows a crystal plane does not appear. A halo pattern is shown in anelectron diffraction pattern of the amorphous oxide semiconductor film.Further, a halo pattern is shown but a spot is not shown in a nanobeamelectron diffraction pattern of the amorphous oxide semiconductor film.

Note that an oxide semiconductor film may have a structure havingphysical properties between the nc-OS film and the amorphous oxidesemiconductor film. The oxide semiconductor film having such a structureis specifically referred to as an amorphous-like oxide semiconductor(a-like OS) film.

In a high-resolution TEM image of the a-like OS film, a void is observedin some cases. Furthermore, in the high-resolution TEM image, there area region where a crystal part is clearly observed and a region where acrystal part is not observed. In the a-like OS film, crystallizationoccurs by a slight amount of electron beam used for TEM observation andgrowth of the crystal part is found in some cases. In contrast,crystallization by a slight amount of electron beam used for TEMobservation is hardly observed in the nc-OS film having good quality.

Note that the crystal part size in the a-like OS film and the nc-OS filmcan be measured using high-resolution TEM images. For example, anInGaZnO₄ crystal has a layered structure in which two Ga—Zn—O layers areincluded between In—O layers. A unit cell of the InGaZnO₄ crystal has astructure in which nine layers of three In—O layers and six Ga—Zn—Olayers are layered in the c-axis direction. Accordingly, the spacingbetween these adjacent layers is equivalent to the lattice spacing onthe (009) plane (also referred to as d value). The value is calculatedto 0.29 nm from crystal structure analysis. Thus, focusing on latticefringes in the high-resolution TEM image, each of lattice fringes inwhich the lattice spacing therebetween is greater than or equal to 0.28nm and less than or equal to 0.30 nm corresponds to the a-b plane of theInGaZnO₄ crystal.

Note that an oxide semiconductor film may be a stacked film includingtwo or more films of an amorphous oxide semiconductor film, an a-like OSfilm, a microcrystalline oxide semiconductor film, and a CAAC-OS film,for example.

The structure described in this embodiment can be used in appropriatecombination with the structure described in any of the otherembodiments.

Embodiment 6

In this embodiment, a display module which can be formed using a displaydevice of one embodiment of the present invention will be described.

In a display module 8000 in FIG. 25, a touch panel 8004 connected to anFPC 8003, a display panel 8006 connected to an FPC 8005, a backlightunit 8007, a frame 8009, a printed circuit board 8010, and a battery8011 are provided between an upper cover 8001 and a lower cover 8002.

The display device of one embodiment of the present invention can beused for, for example, the display panel 8006.

The shapes and sizes of the upper cover 8001 and the lower cover 8002can be changed as appropriate in accordance with the sizes of the touchpanel 8004 and the display panel 8006. The upper cover 8001 and thelower cover 8002 have flexibility.

The touch panel 8004 is, typically, a resistive touch panel or acapacitive touch panel and overlaps with the display panel 8006. Acounter substrate (sealing substrate) of the display panel 8006 can havea touch panel function. A photosensor may be provided in each pixel ofthe display panel 8006 so that the touch panel 8004 can function as anoptical touch panel. The touch panel 8004 may have flexibility. Thefunction of the touch panel may be achieved by the use of the distortionsensor element of one embodiment of the present invention.

The backlight unit 8007 includes a light source 8008. Note that althougha structure in which the light sources 8008 are provided over thebacklight unit 8007 is illustrated in FIG. 25, one embodiment of thepresent invention is not limited to this structure. For example, astructure in which a light source 8008 is provided at an end portion ofthe backlight unit 8007 and a light diffusion plate is further providedmay be employed. In the case where a self-luminous light-emittingelement such as an organic EL element is used or the case where areflective panel is used, the backlight unit 8007 is not necessarilyprovided. The backlight unit 8007 may have flexibility.

The frame 8009 protects the display panel 8006 and functions as anelectromagnetic shield for blocking electromagnetic waves generated bythe operation of the printed circuit board 8010. The frame 8009 canfunction as a radiator plate. The frame 8009 may have flexibility.

The printed circuit board 8010 has a power supply circuit and a signalprocessing circuit for outputting a video signal and a clock signal. Asa power source for supplying power to the power supply circuit, anexternal commercial power source or a power source using the battery8011 provided separately may be used. The battery 8011 can be omitted inthe case of using a commercial power source. The printed circuit board8010 may be an FPC.

The display module 8000 may be additionally provided with a member suchas a polarizing plate, a retardation plate, or a prism sheet.

The structure described in this embodiment can be used in appropriatecombination with the structure described in any of the otherembodiments.

Embodiment 7

In this embodiment, a touch panel that can include a display deviceprovided with the distortion sensor of one embodiment of the presentinvention will be described.

The touch panel of one embodiment of the present invention includes anactive matrix touch sensor, a display element, and a distortion sensorelement between a pair of substrates. The touch sensor is a capacitivetype touch sensor, for example. The touch panel allows not only input bylocal touch on a display portion but also input by bending of thedisplay portion owing to the distortion sensor element. Note that thedescription of the distortion sensor element in the above embodiment isnot made below.

In a touch panel including a touch sensor portion and a display portionthat overlap with each other, a parasitic capacitance is formed in somecases between a wiring or an electrode included in a capacitive typetouch sensor and a wiring or an electrode included in the displayportion. Noise caused by operating the display element travels to thetouch sensor side through the parasitic capacitance and the detectionsensitivity of the touch sensor might decrease.

By sufficiently increasing the distance between the touch sensor portionand the display portion, the adverse effect of the noise can be avoidedand the decrease in the detection sensitivity of the touch sensor can besuppressed; however, the thickness of the whole touch panel is increasedin some cases.

In one embodiment of the present invention, an active matrix touchsensor is provided. The touch sensor includes a transistor and acapacitor. The transistor and the capacitor are electrically connectedto each other.

In the active matrix touch sensor of one embodiment of the presentinvention, an electrode of a capacitor and a read wiring can be formedin different layers. When the read wiring has a narrow width, aparasitic capacitance can be small and the adverse effect of the noisecan be suppressed. Accordingly, a decrease in the detection sensitivityof the touch sensor can be suppressed. In addition, by amplifying adetection signal and outputting the amplified signal, the adverse effectof the noise can be suppressed.

An active matrix touch sensor is used in the touch panel of oneembodiment of the present invention, whereby the distance between thesensor portion and the display portion can be reduced in the touchpanel, and the touch panel can have a small thickness. Furthermore, thetouch sensor and the display element can be located between twosubstrates, whereby the touch panel can have a small thickness. Here,using the touch sensor of one embodiment of the present invention cansuppress a decrease in the detection sensitivity of the touch sensoreven when the distance between the sensor portion and the displayportion is reduced. Therefore, in one embodiment of the presentinvention, both a small thickness and high detection sensitivity of atouch sensor or a touch panel can be achieved. Furthermore, by using aflexible material for the pair of substrates of the touch panel, thetouch panel can have flexibility. Furthermore, in one embodiment of thepresent invention, a touch panel with high resistance to repeatedbending can be provided. Furthermore, a large-sized touch panel can beprovided.

The touch sensor included in the touch panel of one embodiment of thepresent invention may include an oxide conductor layer as the electrodeof the capacitor. In the active matrix touch sensor, a semiconductorlayer and a conductive film of the transistor and the electrode of thecapacitor are preferably formed in the same step. Thus, the number ofsteps of manufacturing the touch panel can be reduced and the cost ofmanufacturing the touch panel can be reduced.

Note that because the oxide conductor layer is used as the electrode ofthe capacitor in the touch panel of one embodiment of the presentinvention, viewing angle dependence is smaller than that of a touchpanel using another material as the electrode of the capacitor in somecases. Furthermore, because the oxide conductor layer is used as theelectrode of the capacitor in the touch panel of one embodiment of thepresent invention, an NTSC ratio can be higher than that of a touchpanel using another material as the electrode of the capacitor in somecases.

Specifically, one embodiment of the present invention is a touch panelincluding a touch sensor, a light-blocking layer, and a display element.In the touch panel, the light-blocking layer is located between thetouch sensor and the display element, the light-blocking layer includesa portion overlapping with a transistor included in the touch sensor,and the display element includes a portion overlapping with a capacitorincluded in the touch sensor. Note that the touch panel allows datainput without contact.

The display element can be, but is not particularly limited to, anorganic EL element.

<Structure Example of Touch Panel>

FIGS. 26A and 26B are a projection view and a perspective viewillustrating components of a touch panel of one embodiment of thepresent invention. FIG. 26A is a projection view illustrating componentsof a touch panel 700 of one embodiment of the present invention and asensor unit 800 included in the touch panel 700.

The touch panel 700 described in this embodiment includes a flexibleinput device 100 and a display portion 701 (see FIGS. 26A and 26B). Theflexible input device 100 is provided with a plurality of sensor units800 arranged in matrix and including window portions 14 that transmitvisible light; a scan line G1 electrically connected to the plurality ofsensor units 800 arranged in the row direction (shown by an arrow R inFIG. 26A); a signal line DL electrically connected to the plurality ofsensor units 800 arranged in the column direction (shown by an arrow Cin FIG. 26A); and a flexible base material 16 supporting the sensorunits 800, the scan line G1, and the signal line DL. The display portion701 is provided with a plurality of pixels 702 overlapping with thewindow portions 14 and arranged in matrix; and a flexible base material710 supporting the pixels 702.

The sensor unit 800 includes a sensor element C overlapping with thewindow portion 14 and a sensor circuit 19 electrically connected to thesensor element C (FIG. 26A).

The sensor circuit 19 is supplied with a selection signal, and suppliesa sensor signal DATA in accordance with a change in capacitance of thesensor element C.

The scan line G1 can supply a selection signal. The signal line DL cansupply the sensor signal DATA. The sensor circuit 19 is provided so asto overlap with a gap between the window portions 14.

In addition, the touch panel 700 described in this embodiment includes acoloring layer between the sensor unit 800 and the pixel 702 overlappingwith the window portion 14 of the sensor unit 800.

The touch panel 700 described in this embodiment includes the flexibleinput device 100 including the plurality of sensor units 800, each ofwhich is provided with the window portions 14 transmitting visiblelight, and the flexible display portion 701 including the plurality ofpixels 702 overlapping with the window portions 14. The coloring layeris included between the window portion 14 and the pixel 702.

With such a structure, the touch panel can supply a sensor signal basedon the change in the capacitance and positional data of the sensor unitsupplying the sensor signal, can display image data associated with thepositional data of the sensor unit, and can be bent. As a result, anovel touch panel with high convenience or high reliability can beprovided.

The touch panel 700 may include a flexible substrate FPC1 to which asignal from the input device 100 is supplied and/or a flexible substrateFPC2 supplying a signal including image data to the display portion 701.

In addition, a protective layer 17 p protecting the touch panel 700 bypreventing damage and/or an anti-reflective layer 767 p that weakens theintensity of external light reflected by the touch panel 700 may beincluded.

Moreover, the touch panel 700 includes a scan line driver circuit 703 gwhich supplies the selection signal to a scan line of the displayportion 701, a wiring 711 supplying a signal, and a terminal 719electrically connected to the flexible substrate FPC2.

Components of the touch panel 700 are described below. Note that thesecomponents cannot be clearly distinguished and one component also servesas another component or includes part of another component in somecases.

For example, the input device 100 including the coloring layeroverlapping with the plurality of window portions 14 also serves as acolor filter.

Furthermore, for example, the touch panel 700 in which the input device100 overlaps the display portion 701 serves as the input device 100 aswell as the display portion 701.

The touch panel 700 includes the input device 100 and the displayportion 701 (FIG. 26A).

The input device 100 includes the plurality of sensor units 800 and theflexible base material 16 supporting the sensor units. For example, theplurality of sensor units 800 are arranged in matrix with 40 rows and 15columns on the flexible base material 16.

The window portion 14 transmits visible light.

For example, the window portion 14 may be formed as follows: the basematerial 16, the sensor element C, and a flexible protective basematerial 17 each formed using a material transmitting visible light or amaterial thin enough to transmit visible light overlap with each othersuch that transmission of visible light is not prevented.

For example, an opening portion may be provided in a material that doesnot transmit visible light. Specifically, one opening portion or aplurality of opening portions having any of a variety of shapes such asa rectangle may be provided.

A coloring layer that transmits light of a predetermined color isprovided to overlap with the window portion 14. For example, a coloringlayer CFB transmitting blue light, a coloring layer CFG transmittinggreen light, and a coloring layer CFR transmitting red light areincluded (FIG. 26A).

Note that in addition to the coloring layers transmitting blue light,green light, and/or red light, coloring layers transmitting light ofvarious colors such as a coloring layer transmitting white light and acoloring layer transmitting yellow light can be included.

For a coloring layer, a metal material, a resin material, a pigment,dye, or the like can be used.

A light-blocking layer BM is provided to surround the window portions14. The light-blocking layer BM does not easily transmit light ascompared to the window portion 14. Note that in an example illustratedin this specification and the like, a black matrix is used as thelight-blocking layer, and the letter symbol BM is used to denote thelight-blocking layer.

For the light-blocking layer BM, carbon black, a metal oxide, acomposite oxide containing a solid solution of a plurality of metaloxides, or the like can be used.

The scan line G1, the signal line DL, a wiring VPI, a wiring RES, awiring VRES, and the sensor circuit 19 are provided to overlap with thelight-blocking layer BM.

Note that a light-transmitting overcoat covering the coloring layer andthe light-blocking layer BM can be provided.

As the flexible base material 16 and the flexible base material 710, anorganic material, an inorganic material, or a composite material of anorganic material and an inorganic material can be used.

For the base material 16 and the base material 710, a material with athickness of 5 μm or more and 2500 μm or less, preferably 5 μm or moreand 680 μm or less, further preferably 5 μm or more and 170 μm or less,still further preferably 5 μm or more and 45 μm or less, yet stillfurther preferably 8 μm or more and 25 μm or less can be used.

A material with which passage of impurities is inhibited can befavorably used for the base material 16 and the base material 710. Forexample, a material with a vapor permeability of lower than or equal to10⁻⁵ g/(m²·day), preferably lower than or equal to 10⁻⁶ g/(m²·day) canbe favorably used.

The base material 710 can be favorably formed using a material whosecoefficient of linear expansion is substantially equal to that of thematerial of the base material 16. For example, the base material 710 andthe base material 16 can each be formed using a material whosecoefficient of linear expansion is preferably lower than or equal to1×10⁻³/K, further preferably lower than or equal to 5×10⁻⁵/K, and stillfurther preferably lower than or equal to 1×10⁻⁵/K.

Examples of the materials of the base material 16 and the base material710 are organic materials such as a resin, a resin film, and a plasticfilm.

Examples of the materials of the base material 16 and the base material710 are inorganic materials such as a metal plate and a thin glass platewith a thickness of more than or equal to 10 μm and less than or equalto 50 μm.

The input device 100 can include the flexible protective base material17 and/or the protective layer 17 p. The flexible protective basematerial 17 or the protective layer 17 p protects the input device 100by preventing damage.

The display portion 701 includes a plurality of pixels 702 arranged inmatrix (FIG. 26B). For example, the pixel 702 includes a sub-pixel 702B,a sub-pixel 702G, and a sub-pixel 702R, and each sub-pixel includes adisplay element and a pixel circuit for driving the display element.

Note that in the pixel 702, the sub-pixel 702B is located to overlapwith the coloring layer CFB, the sub-pixel 702G is located to overlapwith the coloring layer CFG, and the sub-pixel 702R is located tooverlap with the coloring layer CFR.

The display portion 701 may include the anti-reflective layer 767 ppositioned in a region overlapping with pixels. As the anti-reflectivelayer 767 p, a circular polarizing plate can be used, for example.

The display portion 701 includes the wiring 711 through which a signalcan be supplied. The wiring 711 is provided with the terminal 719. Notethat the flexible substrate FPC2 through which a signal such as an imagesignal or a synchronization signal can be supplied is electricallyconnected to the terminal 719.

Note that a printed wiring board (PWB) may be attached to the flexiblesubstrate FPC2.

<<Sensor Element C>>

The sensor element C is described giving an example that uses acapacitor. The capacitor includes a pair of electrodes. The capacitorincludes an insulating film as the dielectric layer between the pair ofelectrodes.

When an object whose dielectric constant is different from that of theair gets closer to one of the pair of electrodes of the sensor element Cthat is put in the air, the capacitance of the sensor element C ischanged. Specifically, when a finger or the like gets closer to thesensor element C, the capacitance of the sensor element C is changed.Thus, the sensor element C can be used in a proximity sensor.

When the sensor element C is changed in shape, the capacitance ischanged with the change in shape.

Specifically, when a finger or the like is in contact with the sensorelement C, and the gap between the pair of electrodes becomes small, thecapacitance of the sensor element C is increased. Accordingly, thesensor element C can be used in a tactile sensor.

Specifically, when the sensor element C is bent, and the gap between thepair of electrodes becomes small, the capacitance of the sensor elementC is increased. Accordingly, the sensor element C can also be used in abend sensor.

<<Sensor Circuit 19 and Converter CONV>>

FIGS. 27A, 27B1, 27B2, and 27C illustrate configurations of the sensorcircuit 19 and a converter CONV and a driving method of the sensorcircuit 19 that are embodiments of the present invention.

FIG. 27A is a circuit diagram illustrating configurations of the sensorcircuit 19 and the converter CONV of embodiments of the presentinvention, and FIGS. 27B 1 and 27B2 are timing charts illustrating adriving method of one embodiment of the present invention. FIG. 27Cshows the converter CONV that is different from the converter CONV shownin FIG. 27A. FIG. 28A shows the sensor circuits 19 in matrix.

The sensor circuit 19 includes transistors M1 to M3, for example (FIG.27A and FIG. 28A). In addition, the sensor circuit 19 includes wiringsthat supply a power supply potential and a signal. For example, thesignal line DL, the wiring VPI, a wiring CS, the scan line G1, thewiring RES, the wiring VRES, and the like are included.

Note that the sensor circuit 19 may be located not to overlap with thewindow portion 14.

Furthermore, the transistors M1 to M3 each include a semiconductorlayer. For example, for the semiconductor layer, an element belonging toGroup 14, a compound semiconductor, or an oxide semiconductor can beused. Specifically, a semiconductor containing silicon, a semiconductorcontaining gallium arsenide, an oxide semiconductor containing indium,or the like can be used.

Transistors that can be formed in the same process can be used as thetransistors M1 to M3.

Any one of the transistors M1 to M3 preferably includes an oxidesemiconductor layer. At this time, the oxide semiconductor layer and theoxide conductor layer are preferably located over the same surface. Theoff-state current of a transistor including an oxide semiconductor layeris small; therefore, it is particularly preferable that the transistorM1 include the oxide semiconductor layer.

For the wiring, a conductive material can be used. For example, aninorganic conductive material, an organic conductive material, a metalmaterial, a conductive ceramic material, or the like can be used for thewiring. Specifically, a material that is the same as those of the pairof electrodes of the capacitor can be used.

For the scan line G1, the signal line DL, the wiring VPI, the wiringRES, and the wiring VRES, a metal material such as aluminum, gold,platinum, silver, nickel, titanium, tungsten, chromium, molybdenum,iron, cobalt, copper, or palladium, or an alloy material containing anyof these metal materials can be used.

The sensor circuit 19 may be formed over the base material 16 byprocessing a film formed over the base material 16.

Alternatively, the sensor circuit 19 formed over another base materialmay be transferred to the base material 16.

Various circuits that can convert the sensor signal DATA supplied fromthe sensor unit 800 and supply the converted signal to the flexiblesubstrate FPC1 can be used as the converter CONV (FIG. 26A). Forexample, a transistor M4 can be used in the converter CONV. Furthermore,as shown in FIG. 27C, the transistor M4 and a transistor M5 can be usedin the converter CONV.

The sensor circuit 19 of one embodiment of the present inventionincludes the transistor M1 whose gate is electrically connected to oneelectrode of the sensor element C and whose first electrode iselectrically connected to the wiring VPI that can supply a groundpotential, for example (see FIG. 27A).

The sensor circuit 19 may further include the transistor M2 whose gateis electrically connected to the scan line G1 that can supply aselection signal, whose first electrode is electrically connected to asecond electrode of the transistor M1, and whose second electrode iselectrically connected to the signal line DL that can supply the sensorsignal DATA, for example.

The sensor circuit 19 may further include the transistor M3 whose gateis electrically connected to the wiring RES that can supply a resetsignal, whose first electrode is electrically connected to the oneelectrode of the sensor element C, and whose second electrode iselectrically connected to the wiring VRES that can supply, for example,a ground potential.

The capacitance of the sensor element C is changed when an object getsclose to the pair of electrodes or when the distance between the pair ofelectrodes is changed. Thus, the sensor circuit 19 can supply the sensorsignal DATA based on a change in the capacitance of the sensor elementC.

The sensor circuit 19 is provided with the wiring CS that can supply acontrol signal for controlling the potential of the other electrode ofthe sensor element C.

Note that a node at which the one electrode of the sensor element C, thegate of the transistor M1, and the first electrode of the transistor M3are electrically connected to one another is referred to as a node A.

The wiring VRES and wiring VPI each can supply a ground potential, forexample, and a wiring VPO and a wiring BR each can supply a high powersupply potential, for example. Furthermore, the wiring RES can supplythe reset signal, and the scan line G1 can supply the selection signal.Furthermore, the signal line DL can supply the sensor signal DATA, and aterminal OUT can supply a signal converted based on the sensor signalDATA.

Any of various circuits that can convert the sensor signal DATA andsupply the converted signal to the terminal OUT can be used as theconverter CONV. For example, a source follower circuit, a current mirrorcircuit, or the like may be formed by the electrical connection betweenthe converter CONV and the sensor circuit 19.

Specifically, by using the converter CONV including the transistor M4, asource follower circuit can be formed (FIG. 27A). Furthermore, as shownin FIG. 27C, the converter CONV may include the transistors M4 and M5.Note that transistors that can be formed in the same process as those ofthe transistor M1 to the transistor M3 may be used as the transistors M4and M5.

As described above, in the active matrix touch sensor of one embodimentof the present invention, the electrode of the sensor element and theread wiring can be formed in different layers. As shown in FIG. 28B, oneelectrode CM of a capacitor and a wiring ML are formed in differentlayers, and the width of the wiring ML is made narrow. Thus, theparasitic capacitance can be small and the adverse effect of noise canbe suppressed. Accordingly, a decrease in the detection sensitivity ofthe touch sensor can be suppressed. Note that the one electrode CM ofthe capacitor overlaps with the plurality of pixels 702 shown in FIG.28C that is an enlarged view of FIG. 28B.

<Driving Method of Sensor Circuit 19>

A driving method of the sensor circuit 19 is described.

<<First Step>>

In a first step, after the transistor M3 is turned on, a reset signalfor turning off the transistor M3 is supplied to the gate of thetransistor M3, so that the potential of the first electrode of thesensor element C is set to a predetermined potential (see Period T1 inFIG. 27B1).

Specifically, the reset signal is supplied from the wiring RES. Thetransistor M3 supplied with the reset signal renders the potential ofthe node A a ground potential, for example (see FIG. 27A).

<<Second Step>>

In a second step, a selection signal that turns on the transistor M2 issupplied to the gate of the transistor M2, and the second electrode ofthe transistor M1 is electrically connected to the signal line DL.

Specifically, the selection signal is supplied from the scan line G1.Through the transistor M2 to which the selection signal is supplied, thesecond electrode of the transistor M1 is electrically connected to thesignal line DL (see a period T2 in FIG. 27B1).

<<Third Step>>

In a third step, a control signal is supplied to the second electrode ofthe sensor element, and a potential changed in accordance with thecontrol signal and the capacitance of the sensor element C is suppliedto the gate of the transistor M1.

Specifically, a rectangular control signal is supplied from the wiringCS. The sensor element C whose second electrode is supplied with therectangular control signal increases the potential of the node A inaccordance with the capacitance of the sensor element C (see the latterpart of Period T2 in FIG. 27B1).

For example, in the case where the sensor element C is put in the air,when an object whose dielectric constant is higher than that of the airis placed closer to the second electrode of the sensor element C, thecapacitance of the sensor element C is apparently increased.

Thus, the change in the potential of the node A caused by therectangular control signal becomes smaller than that in the case wherean object whose dielectric constant is higher than that of the air isnot placed close to the second electrode of the sensor element C (see asolid line in FIG. 27B2).

<<Fourth Step>>

In a fourth step, a signal obtained by the change in the potential ofthe gate of the transistor M1 is supplied to the signal line DL.

For example, a change in current due to the change in the potential ofthe gate of the transistor M1 is supplied to the signal line DL.

The converter CONV converts the change in the current flowing throughthe signal line DL into a change in voltage and supplies the voltage.

<<Fifth Step>>

In a fifth step, a selection signal for turning off the transistor M2 issupplied to the gate of the transistor M2.

FIG. 29 is a cross-sectional view illustrating the structure of theabove-described touch panel. FIG. 29 illustrates an example in which thedisplay device in FIGS. 3A and 3B is provided with a touch sensor. Inthe touch panel, the transistor of the sensor circuit 19 and a capacitor340 are formed on the second substrate 42 side.

One electrode 341 of the capacitor 340 is formed to overlap with thecoloring layer 336, using a material transmitting the light passingthrough the coloring layer 336. The other electrode 342 of the capacitor340 can be formed using, for example, the same material as asemiconductor layer of the transistor. For example, an oxide conductorlayer formed by adding impurities forming oxygen vacancies, impuritiesforming donor levels, or the like to an oxide semiconductor layer can beused.

The structure described in this embodiment can be used in appropriatecombination with the structure described in any of the otherembodiments.

Embodiment 8

In this embodiment, a structure of a data processing device that caninclude the display device of one embodiment of the present inventionwill be described with reference to FIGS. 30A to 30C.

FIGS. 30A to 30C illustrate a data processing device including thedisplay device of one embodiment of the present invention.

FIG. 30A is a projection view illustrating an input/output device 6020of a data processing device 6000 of one embodiment of the presentinvention that is unfolded. FIG. 30B is a cross-sectional view of thedata processing device 6000 along X1-X2 in FIG. 30A. FIG. 30C is aprojection view illustrating the input/output device 6020 that isfolded.

<Structural Example of Data Processing Device>

The data processing device 6000 described in this embodiment includesthe input/output device 6020 that is supplied with image data V andsupplies sensing data S, and an arithmetic device 6010 that supplies theimage data V and is supplied with the sensing data S.

The input/output device 6020 includes a display portion 6030 that issupplied with the image data V and an input device that supplies thesensing data S. Note that the input device corresponds to the distortionsensor element described in the above embodiment.

The display portion 6030 includes a region 6031 where a first region6031(11), a first bendable region 6031(21), a second region 6031(12), asecond bendable region 6031(22), and a third region 6031(13) arearranged in stripes in this order (see FIG. 30A).

The display portion 6030 can be folded and unfolded along a first foldline formed in the first bendable region 6031(21) and a second fold lineformed in the second bendable region 6031(22) (see FIGS. 30A and 30C).

The above input device determines whether the input/output device 6020is folded or unfolded and supplies the sensing data S that contains datashowing the determined state.

The arithmetic device 6010 supplies the image data V containing a firstimage to the first region 6031(11) in the case where the sensing data Sshows the folded state, and supplies the image data V to the displayregion 6031 of the display portion 6030 in the case where the sensingdata S shows the unfolded state (see FIGS. 30A to 30C).

The data processing device 6000 described in this embodiment includesthe input/output device 6020 and the arithmetic device 6010. Theinput/output device 6020 is foldable and supplied with the image data V.The arithmetic device 6010 supplies the image data V and is suppliedwith the sensing data S. The input/output device 6020 includes the inputdevice that determines whether the input/output device 6020 is folded orunfolded and supplies the sensing data S containing the data showing thedetermined state.

With such a structure, the first image can be displayed on the firstregion 6031(11) of the folded display portion, and a second image can bedisplayed on a display region of the unfolded display portion 6030 (seeFIG. 30A). As a result, a novel data processing device with highconvenience or high reliability can be provided.

A housing 6001(1), a hinge 6002(1), a housing 6001(2), a hinge 6002(2),and a housing 6001(3) are positioned in this order such that theinput/output device 6020 can be held, folded, and unfolded (see FIG.30B).

In the example described in this embodiment, the data processing devicehas the three housings connected with one another with the two hinges.The data processing device having this structure can be folded with theinput/output device 6020 bent at two positions.

Note that n housings (n is a natural number of two or more) may beconnected with one another with (n−1) hinges. The data processing devicehaving this structure can be folded with the input/output device 6020bent at (n−1) positions.

Note that the input/output device 6020 or another sensor may sense thestate where the input/output device 6020 is folded or unfolded and maysupply data indicating that the input/output device 6020 is folded. Thearithmetic device 6010 to which data indicating that the input/outputdevice 6020 is folded may stop operation of the portion that is foldedinside. Specifically, operation of the display portion 6030 and/or theinput device may be stopped. Accordingly, the user of the dataprocessing device 6000 can reduce power wasted by an unavailable portion(portion folded inside).

The display device of one embodiment of the present invention canself-detect the shape of the display portion with the use of thedistortion sensor element. Therefore, the data processing device in thisembodiment, which can be folded into two or more, can automaticallydisplay an image appropriate for the shape of the display portion.

The housing 6001(1) overlaps with the first region 6031(11) and isprovided with a button 6045(1).

The housing 6001(2) overlaps with the second region 6031(12).

The housing 6001(3) overlaps with the third region 6031(13). Thearithmetic device 6010, an antenna 6010A, and a battery 6010B areprovided in the housing 6001(3).

The hinge 6002(1) overlaps with the first bendable region 6031(21) androtatably connects the housing 6001(1) to the housing 6001(2).

The hinge 6002(2) overlaps with the second bendable region 6031(22) androtatably connects the housing 6001(2) to the housing 6001(3).

The antenna 6010A is electrically connected to the arithmetic device6010 and supplies or is supplied with a signal.

In addition, the antenna 6010A is wirelessly supplied with power from anexternal device and supplies the power to the battery 6010B.

The battery 6010B is electrically connected to the arithmetic device6010 and supplies or is supplied with power.

The structure described in this embodiment can be used in appropriatecombination with the structure described in any of the otherembodiments.

Embodiment 9

In this embodiment, electronic devices to which one embodiment of thepresent invention is applied will be described with reference to FIGS.31A to 31D.

Highly reliable flexible electronic devices can be manufactured byadopting the display device of one embodiment of the present invention.

Examples of the electronic devices are a television device, a monitor ofa computer or the like, digital signage, a camera such as a digitalcamera or a digital video camera, a digital photo frame, a mobile phone,a portable game console, a portable information terminal, an audioreproducing device, a large-sized game machine, and the like.

The display device of one embodiment of the present invention hasflexibility and thus can be incorporated along a curved inside/outsidewall surface of a house or a building or a curved interior/exteriorsurface of a car. The display device of one embodiment of the presentinvention can be folded or rolled up to be carried.

FIG. 31A illustrates an example of a thin portable information terminal.A portable information terminal 7100 includes a display portion 7102incorporated in a housing 7101, a speaker 7105, a microphone 7106, acamera 7107, and the like. Note that the housing 7101, the displayportion 7102, and the like are flexible, whereby the portableinformation terminal 7100 achieves excellent portability and highresistance against shock such as a drop impact. The display portion 7102includes the display device of one embodiment of the present invention,and for example, images can be switched in bending of the displayportion.

FIG. 31B illustrates an example of a large-sized display such as atelevision or digital signage. A large-sized display 7200 includes aflexible housing 7201 and a display portion 7202 including the displaydevice of one embodiment of the present invention. The large-sizeddisplay 7200 can be folded or rolled up. Even when the large-sizeddisplay is curved as shown in the drawing, image display can beperformed with viewability as high as that in the case where the displayis flat. In addition, when a sensor 7203 sensing the position of aviewer operates, an image with high viewability can be displayed to onlya specific viewer.

FIG. 31C illustrates an example of an armband with a display function.An armband 7300 includes a tube-shaped flexible body 7301 formed using acloth, a resin, or the like and a display portion 7302 including thedisplay device of one embodiment of the present invention. The armband7300 is foldable. Displayed images can be enlarged or reduced inaccordance with the degree of curvature, so that an image with highviewability can be displayed.

FIG. 31D illustrates an example of clothing with a display function.Clothing 7400 includes flexible fabric 7401 and a display portion 7402including the display device of one embodiment of the present invention.The clothing 7400 can be easily changed in shape and folded. Since thedisplay device can self-detect its shape, an image with high viewabilitycan be displayed in a specific direction regardless of the amount ofchange in shape of the clothing 7400.

The structure described in this embodiment can be used in appropriatecombination with the structure described in any of the otherembodiments.

This application is based on Japanese Patent Application serial no.2014-086089 filed with Japan Patent Office on Apr. 18, 2014 and JapanesePatent Application serial no. 2014-095331 filed with Japan Patent Officeon May 2, 2014 the entire contents of which are hereby incorporated byreference.

What is claimed is:
 1. A display device comprising: a first substratehaving flexibility; a second substrate having flexibility; and a pixelportion including a plurality of pixels arranged in matrix, the pixelportion comprising: a pixel circuit portion in a pixel of the pluralityof pixels between the first substrate and the second substrate; and adistortion sensor circuit portion between the first substrate and thesecond substrate, wherein the distortion sensor circuit portion is overthe pixel circuit portion, wherein the pixel circuit portion comprises afirst transistor and a display element electrically connected to thefirst transistor, wherein the distortion sensor circuit portioncomprises a sensor element, and wherein the sensor element is configuredto sense distortion of the first substrate or the second substrate. 2.The display device according to claim 1, wherein the distortion sensorcircuit portion comprises a second transistor, and wherein the secondtransistor is electrically connected to the sensor element.
 3. Thedisplay device according to claim 2, wherein the first transistor andthe second transistor each comprise a channel formation region comprisesan oxide semiconductor.
 4. The display device according to claim 3,wherein the oxide semiconductor comprises In, Zn, and M, and wherein Mis Al, Ti, Ga, Sn, Y, Zr, La, Ce, Nd, or Hf.
 5. The display deviceaccording to claim 3, wherein the oxide semiconductor comprises a c-axisaligned crystal.
 6. The display device according to claim 1, wherein thesensor element is a metal thin film resistor.
 7. The display deviceaccording to claim 1, wherein the display element is an organic ELelement.
 8. A display module comprising: the display device according toclaim 1; and a flexible printed circuit or a frame.
 9. An electronicdevice comprising: the display device according to claim 1; and aspeaker, a microphone, or a camera.
 10. The display device according toclaim 1, further comprising a sealing layer over the display element,wherein the sensor element is over the sealing layer.
 11. A displaydevice comprising: a first substrate having flexibility; a secondsubstrate having flexibility; and a pixel portion including a pluralityof pixels arranged in matrix, the pixel portion comprising: a pixelcircuit portion in a pixel of the plurality of pixels between the firstsubstrate and the second substrate; and a distortion sensor circuitportion between the first substrate and the second substrate, whereinthe pixel circuit portion comprises a first transistor and a displayelement electrically connected to the first transistor, wherein thedistortion sensor circuit portion comprises a second transistor and asensor element electrically connected to the second transistor, whereinthe pixel circuit portion is electrically connected to the distortionsensor circuit portion, and wherein the sensor element is configured tosense distortion of the first substrate or the second substrate.
 12. Thedisplay device according to claim 11, wherein the first transistor andthe second transistor each comprise a channel formation region comprisesan oxide semiconductor.
 13. The display device according to claim 12,wherein the oxide semiconductor comprises In, Zn, and M, and wherein Mis Al, Ti, Ga, Sn, Y, Zr, La, Ce, Nd, or Hf.
 14. The display deviceaccording to claim 12, wherein the oxide semiconductor comprises ac-axis aligned crystal.
 15. The display device according to claim 11,wherein the sensor element is a metal thin film resistor.
 16. Thedisplay device according to claim 11, wherein the display element is anorganic EL element.
 17. A display module comprising: the display deviceaccording to claim 11; and a flexible printed circuit or a frame.
 18. Anelectronic device comprising: the display device according to claim 11;and a speaker, a microphone, or a camera.
 19. The display deviceaccording to claim 11, further comprising an insulating film over thefirst transistor and the second transistor, wherein the display elementand the sensor element are over the insulating film.
 20. The displaydevice according to claim 11, wherein the sensor element is electricallyconnected to a resistor, and wherein the resistor is electricallyconnected to the display element.